Chapter XX: Appendix: To the Fishes: Palaeospondylidae—ostracodermi—heterostraci (1)

OSTEOSTRACI—ANASPIDA—ANTIARCHI—ARTHRODIRA.

In this chapter it is proposed to treat of certain fossil "Fishes" which, from our ignorance of much that is essential to a proper estimate of their true relationships, cannot at present be referred to any of the recognised primary groups of Fishes.

I. PALAEOSPONDYLIDAE.

The interesting little fossil, _Palaeospondylus gunni_,[615] discovered in the Lower Old Red Sandstone of Caithness, and first described by Traquair, represents the calcified endoskeleton of an elongated fish-like organism about an inch, or not exceeding two inches, in length. The vertebral column consists of a series of broad, calcified ring-like centra, destitute of ribs, but possessing neural arches and spines, and in the caudal region haemal arches and spines in addition. The skull, of which only the ventral surface is known, has a complete basis cranii, laterally expanded behind by periotic capsules, and in front by what seem to be bulging olfactory capsules. Anteriorly, the skull terminates in a ring of calcified cirri. Behind the skull there are two singular post-occipital plates, one on each side of the anterior section of the vertebral column. The tail was apparently furnished with a fringing caudal fin, supported dorsally by the long forked, neural spines, and below by the much shorter haemal spines. There is no trace {522}of limbs, limb-girdles, jaws, or branchial arches, nor any evidence of the existence of scales, denticles, or other exoskeletal structures.

_Palaeospondylus_ has been regarded as a Cyclostome, a view which derives its principal support from the resemblance of the cirri-encircled orifice at the anterior end of the skull to an unpaired nasal or naso-pituitary aperture, and perhaps some measure of credence from such purely negative evidence as the apparent want of limbs, and of any structures comparable to jaws. But even if it be admitted that there is some reason for this view, it is certain that _Palaeospondylus_ obtained a far higher grade of specialisation in certain respects than any of the existing Cyclostomata; the presence of calcified vertebral centra and neural arches is conclusive on this point.[616] _Palaeospondylus_ has also been compared with a larval Arthrodiran and with a larval Dipnoid.[617]

II. OSTRACODERMI.

The Palaeozoic fish-like forms, which, more as a matter of convenience than as an expression of real kinship, it has been customary to include in this group, are amongst the earliest Craniates of which we have any precise knowledge. {523}Of the three subordinate groups or "Orders" into which they have usually been divided hitherto, two, the Heterostraci and the Osteostraci, may, with some show of reason, be considered as related forms, and although they are characterised by much specialisation on independent lines, there is yet some evidence of connecting links between the two. The organisms comprising the third group, the Antiarchi, stand upon a very different footing, and at present it cannot be said that they are in any way related to either the Heterostraci or the Osteostraci, or indeed to any other Craniates whatsoever. The association of the Ostracodermi with the Cyclostomata, a view which has received more influential support than it deserves, is based on the presumed absence of jaws and paired fins. The absence of jaws, which, if present, were almost certainly cartilaginous, has yet to be proved, and even in the latter group it is by no means certain that they do not possess structures which, morphologically if not functionally, are veritable jaws. Nor is it quite certain that the lateral lobes of some Ostracodermi are neither pectoral flaps nor lateral fin-folds, to say nothing of the lateral appendages of the Antiarchi. And to these objections there is the further difficulty that there is absolutely no evidence that the Ostracodermi are monorhinal in the sense in which this term is applied to the Cyclostomata.[618] On these grounds it would seem more in accordance with our present knowledge to regard the Ostracodermi as an independent group whose exact position in the system has yet to be determined, including, however, besides the generally accepted orders Heterostraci and Osteostraci, the recently founded provisional order Anaspida, but excluding the Antiarchi as a separate and distinct section; rather than to crystallise in a definite system of classification views which are either purely conjectural or wholly unjustifiable. Even with this limitation the Ostracodermi are by no means easy to define, especially if we include those remarkable shark-like forms from the Upper Silurian rocks of the south of Scotland which have been so admirably described in the recent classical memoirs of Dr. Traquair. As a rule, the head and the anterior part of the body are laterally expanded, and more or less sharply defined from the rest of the body by prominent postero-lateral angles. The exoskeleton, which exhibits an extraordinary variety of {524}structure in the different families, ranges from a uniform covering of dermal denticles to a condition in which the denticles fuse to form anteriorly a highly characteristic tessellated or continuous dorsal shield, while posteriorly they become replaced by a nearly typical rhombic squamation. The tail is heterocercal. Paired fins of the ordinary piscine type are absent. In some Ostracodermi it seems probable that the gill-clefts opened into a common branchial chamber on each side, with a single external aperture, but in others they may have been ventral. The endoskeleton, jaws, dentition, and the nostrils are unknown.

ORDER I. HETEROSTRACI.

The exoskeletal structures consist of dentine, or of a tissue resembling it, never of true bone. The orbits are marginal or lateral in position. With the exception of a caudal fin there are no median fins.

FAM. 1. COELOLEPIDAE.[619]—Head and anterior portion of the body flattened and expanded, with prominent lappet-like postero-lateral lobes, which may represent continuous lateral fin-folds or a very primitive type of pectoral fin. Nothing is known of the mouth, but it must have been ventral, nor of the position of the orbits. Branchial apertures unknown, but transverse markings on each side of the anterior part of _Thelodus pagei_ may be indications of a branchial apparatus. The exoskeleton consists of a uniform covering of hollow pointed spines, devoid of a basal plate and open below (_Lanarkia_); or of minute shagreen-like tubercles (_Thelodus_). The tubercles or spines consist of dentine coated by ganoin. Of the only two known genera, _Thelodus_ is a characteristic Upper Silurian genus {525}from the Ludlow and Downtonian Beds of Lanarkshire. Detached scales are also known in the Upper Silurian of England. One species (_Th. pagei_) occurs in the Lower Old Red Sandstone of Forfarshire, and another (_Th. tulensis_) in the Upper Devonian of Russia. _Lanarkia_ has only been found in the Downtonian Beds. None of the Coelolepidae exceed fourteen to fifteen inches in length.

FAM. 2. DREPANASPIDAE.—This family[620] affords an interesting transition to the more highly specialised and carapaced Pteraspidae. The head and anterior part of the trunk now form a broad oblong shield, rounded in front and abruptly marked off from the tail by conspicuous rounded angles. The exoskeleton is no longer uniform. In the caudal region the scattered spines or shagreen tubercles of the Coelolepids have become transformed into tuberculated quadrangular scales, which are further differentiated along the dorsal and ventral margins into ridge scales or fulcra; and from a similar source by a process of basal fusion a series of larger or smaller dermal plates are formed as components of large dorsal or ventral shields. The dorsal shield (Fig. 314) is formed by a large central plate; the postero-lateral portions by two narrow falciform plates; and the anterior margin by a series of smaller rostral plates. Between the larger plates the shield is completed by numerous {526}small polygonal plates. All the plates are superficially ornamented by small stellate tubercles. The ventral armature (Fig. 315) is similar to the dorsal. A large mental plate forms the hinder margin of the transverse slit-like mouth, the anterior limit of which is defined by the rostral plates already mentioned. Laterally may be seen a pair of small plates (_x_), each perforated by a small aperture, and probably indicating the position of some kind of sense-organ. Posteriorly there is a large median ventral plate, in relation with a pair of anterior and a pair of posterior ventral plates. The areas between the larger plates are filled in by numerous small polygonal plates. It is possible that there is a single external branchial aperture on each side, near the postero-lateral angle of the shield and behind the posterior ventro-lateral plate. The sole representative of the family is _Drepanaspis gemündenensis_, from the Lower Devonian of Gemünden in Rhenish Prussia. Large examples of this fossil must have exceeded two feet in length.

FAM. 3. PSAMMOSTEIDAE.—To this family are referred certain dermal plates occurring, in a more or less fragmentary condition, in the Old Red Sandstone and Devonian formations of Great Britain and Russia. In their size and shape, and in their stellate tubercles, these have been compared to the dorsal, postero-lateral, and ventral plates of {527}_Drepanaspis_. That _Psammosteus_ is closely allied to _Drepanaspis_ seems certain, but for the present the two genera may be retained in separate families.

FAM. 4. PTERASPIDAE.[621]—Until the recent inclusion of the three preceding families, the Pteraspidae were the only representatives of the Heterostraci. In the best known genus, _Pteraspis_, there is a marked reduction in the number of the component plates of the carapace, and only seven can now be distinguished (Fig. 316): (_a_) a large posterior dorsal plate, supporting behind a stout spine; (_b_) a conical rostral plate, covering the preorbital part of the head; (_c_) a pair of small marginal orbital plates, each with a small aperture, probably for the eye; (_d_) a pair of posterior lateral or cornual plates, each of which is perforated by a large oblique foramen, conjecturally an external branchial aperture; and (_e_) a large ventral plate. There is probably, also, a small median "parietal," or "pineal," plate, with a pit on its inner surface, situated between the rostral and posterior dorsal plates. Externally the plates are sculptured into fine ridges, which in their minute structure and their crenated free margins are suggestive of linear series of fused denticles. The tail appears to have been invested by imbricated rhombic scales. _Pteraspis_ (Lower Old Red Sandstone of Scotland and England, and the Lower Devonian of Galicia); _Cyathaspis_ (Upper Silurian and Lower Old Red Sandstone), known only by its dorsal and ventral shields; and _Holaspis_ (Lower Old Red Sandstone of Monmouthshire, and the Upper Silurian of Pennsylvania), are the only genera.

ORDER II. OSTEOSTRACI.

While agreeing with the more specialised Heterostraci in the division of the body into an anterior carapaced portion and a free {528}hinder part invested by a rhombic squamation, the Osteostraci are distinguished by the presence of bone as a histological component of the dermal hard parts; by the position of the orbits, which, instead of being marginal in position, are close together on the dorsal aspect of the carapace; and by the possession of a median dorsal fin.

FAM. 1. ATELEASPIDAE.[622]—The general shape of the body is much the same as in the Coelolepidae, but the exoskeleton consists of numerous polygonal tuberculated plates in front of the postero-lateral lobes, and of sculptured rhombic scales behind. A pair of crescentic markings, placed close together about the middle of the dorsal surface of the head, probably indicate the outer margins of orbital recesses (Fig. 317). The only species at present known (_Ateleaspis tessellata_) occurs in the Downtonian beds.

FAM. 2. CEPHALASPIDAE.[623]—In this family the dorsal shield is rounded in front, strongly arched above, with its postero-lateral angles produced into highly characteristic cornua (Fig. 318). The shield consists of a single piece, but as the outer surface is ornamented by small tubercles arranged in polygonal areas, it is probable that it has been formed by the basal fusion of {529}numerous primitively distinct polygonal plates (Fig. 319, A). Between the orbits there is a separately calcified but fixed plate, which bears a hollow prominence, probably for the reception of a parietal organ. In some genera certain of the anterior dorsal and ventral scales of the trunk fuse into a continuous plate. Internally to the postero-lateral cornua the middle layer of the shield is prolonged backwards into a pair of singular flap-like lobes, which have been variously interpreted as corresponding to the lateral lobes of the Coelolepidae, to pectoral fins, or to opercula. The scales of the trunk and tail are rhombic and imbricated; on the sides of the body they are remarkably high and narrow.

The best known genus is _Cephalaspis_. The earliest remains are found in the Ludlow Tilestones. The genus is also represented in the Ledbury Passage Beds, the Lower Old Red Sandstone of Scotland, and the Upper and Lower Devonian of Canada. Most of the species are of small size, but _C. magnifica_,[624] from the Caithness Flagstones, the largest of all the Cephalaspids, has a shield 8½ inches long, and 12 inches across the widest part. _Auchenaspis_ occurs in the Ludlow Tilestones and the Ledbury Passage Beds, and also in the Upper Silurian of the Isle of Oesel in the {530}Baltic. Another genus, _Didymaspis_, has been found in the Lower Old Red Sandstone of Ledbury.

FAM. 3. TREMATASPIDAE.—The interorbital plate is free, and hence it is often lost in the fossils. Several species of _Tremataspis_ occur in the Upper Silurian of the Isle of Oesel.

As regards the origin and mutual relationships of the different families comprising the Heterostraci, it has been urged with great force by Dr. Traquair[625] that they constitute a natural sequence of forms, beginning with organisms whose Elasmobranch ancestry is extremely probable, and leading to highly-specialised types, which, considered by themselves, possess little to justify any conclusions whatever as to their origin or kinship. The Coelolepidae form the starting-point, and in the light of their exoskeleton of dermal denticles, their derivation from some primitive Elasmobranch prototype seems a reasonable inference.[626] From the Coelolepids the path of specialisation through the Drepanaspidae and Psammosteidae to the Pteraspidae is marked (i.) by the basal concrescence of isolated denticles to form, first, numerous small polygonal plates, and then larger and less numerous plates, as the constituent elements of a characteristic dorsal shield, leaving, however, the denticles of the rest of the body to become converted into a rhombic squamation; (ii.) by modifications in the "lateral fin-lobes," which may become enclosed in the developing dermal armour (_e.g._ _Drepanaspis_), or cease to be recognisable (_e.g._ _Pteraspis_). The affinities of the Osteostraci are very obscure, and their inclusion with the Heterostraci in the same group (Ostracodermi) has hitherto rested mainly on such negative evidence as the supposed absence of paired limbs, jaws, and teeth; in fact, it has been affirmed that "there is absolutely no reason for regarding _Cephalaspis_ as allied to _Pteraspis_ beyond that the two genera occur in the same rocks."[627] It is possible, however, that in _Ateleaspis_ we have an annectent form, which in some measure combines the structural peculiarities of the two groups. That this singular genus belongs to the Osteostraci is proved by the presence of bone lacunae in its dermal hard parts, a conclusion which is strengthened by the apparently dorsal position of the orbits and the presence of a dorsal fin. On the {531}other hand, its close resemblance to the Coelolepids in the general contour of its laterally-lobed body, and the probability that its mosaic and tuberculated head-shield has been formed by the concrescence of Coelolepid denticles, is at least significant of a relationship to the more primitive Heterostraci. Little can be conjectured as to the habits of these ancient "Fishes." The form and regional proportions of the body, which in some respects often remind one of organisms so diverse as a King Crab, or a Loricaroid Teleost (such as _Liposarcus_), are strongly suggestive of a grovelling, bottom-feeding, sluggish habit of life, in sharp contrast to the more active and predaceous Fishes whose appearance is coincident with the extinction of the Ostracodermi at the close of the Devonian period. Habits such as these may well be associated with much structural degeneration, even, it may be, with the loss of paired fins, and hence it is not altogether improbable that the Ostracodermi are outcasts from the Elasmobranchs, a degenerate race which has sought safety in a sequestered life and a coat of mail.

ORDER III. ANASPIDA.

This group has been instituted by Traquair[628] for the provisional reception of two remarkable genera, which, owing to the absence of precise knowledge of the histology of their exoskeletal structures, cannot at present be referred either to the Heterostraci or the Osteostraci, and for which, as their discoverer remarks, no place can be found in the system unless they are admitted to the Ostracodermi.

FAM. 1. BIRKENIIDAE.—Body fusiform and fish-like. Head bluntly rounded, without a cranial shield. Caudal fin bilobate and heterocercal A median row of scales with recurved spines arranged along the ventral surface. Orbits, jaws, teeth, paired fins, and endoskeleton unknown.

In _Birkenia_ (Fig. 320) the body is invested by longitudinal rows of narrow scales arranged in oblique transverse rows, which are replaced on the head by much smaller, peculiarly disposed, spindle-shaped scutes. On the side of the hinder part of the head there is an oblique row of small apertures, possibly branchial. A small remote dorsal fin, invested by the trunk scales, is present. {532}_Birkenia elegans_, the only species known, does not exceed 3½ inches in length. Less is known about the second genus, _Lasanius_, of which there are two species. Except for the mid-ventral series of spiny scutes, and a row of slender, parallel, rod-like structures, the body appears to have been naked (Fig. 321). The two genera belong to the remarkable series of fossil Fishes from the Silurian rocks of Lanarkshire. Rare in the Ludlow series, _Birkenia_ is by far the most common of the Fishes of the over-lying Downtonian Beds. _Lasanius_ is confined to the latter horizon. _Euphanerops_, from the Upper Devonian of Canada, is probably related to this family, but lateral branchial apertures are not known.[629]

III. ANTIARCHI.

The organisms comprising this group[630] resemble the Ostracodermi in possessing a well-developed carapace of bony plates and a heterocercal tail, as well as in many of the purely negative features which are characteristic of the latter group.

{533}

The remarkable dorsal shield is divided into a small cephalic portion and a much larger hinder part investing the greater part of the trunk, both of which are strongly arched above and flattened ventrally, with a movable articulation between the two. The cephalic shield is formed by numerous symmetrically-disposed tuberculated plates, suturally connected with one another, and, like the other exoskeletal structures, containing bone lacunae (Fig. 322).[631] The orbits are close together, near the middle of the dorsal surface, and between them there is a small median interorbital plate, with a deep pit on its inner surface, possibly for a parietal organ. A small lateral plate (_e.l._), evidently free behind, suggests the presence of an operculum. Nothing is certainly known about the jaws or the nostrils. The mouth is situated just behind the anterior margin of the cephalic shield on the ventral surface, and in front of it there are two plates, {534}which in _Bothriolepis canadensis_ have their oral margins fringed by small "denticles"; it is possible that these plates represent the components of a secondary upper jaw. The dorsal armature of the trunk is shown in Fig. 322. Ventrally it is completed by a pair of anterior ventro-lateral plates and a pair of posterior ventro-lateral plates with a small median plate between the two pairs. Articulating with the anterior ventro-lateral plates by means of a complex hinge joint there is a pair of pectoral appendages of a kind entirely without parallel in any other vertebrated animals. Each appendage is completely encased by numerous suturally connected plates, and about the middle of its length there is a second movable joint. The appendages are hollow, and their cavities probably contained the muscles by which the limbs were moved, and the blood-vessels and nerves for their nutrition and innervation. A lateral line system of the normal type is present in _Pterichthys_, consisting of a lateral groove along the side of the trunk, and of supra-orbital and infra-orbital grooves, and post-temporal and infra-orbital commissures, on the head. The free portion of the body and the tail are invested by imbricated and finely tuberculated scales, which form fulcra in front of and behind the small dorsal fin. There are no pelvic fins. The caudal fin is heterocercal.

FAM. 1. ASTEROLEPIDAE.—The best known genera are _Pterichthys_ from the Lower Old Red Sandstone of Scotland and the Devonian of Eifel, and _Bothriolepis_, a more widely distributed genus which occurs in the Upper Old Red of Scotland and Shropshire, and in the Upper Devonian of Russia and Canada. Two other genera, _Asterolepis_ and _Microbrachius_, are also found in the Old Red Sandstone of Scotland.[632]

Beyond an uncertain and shadowy relationship to the Ostracodermi, and perhaps some points of resemblance to the Arthrodira, the Antiarchi stand alone among Craniates. Nothing is known of their origin; no intermediate forms link them to any other groups, and the high specialisation they have attained is sufficient to negative any idea that they can "be credited with any share in the evolution of the Fishes of more recent periods."

{535}IV. ARTHRODIRA

This group has been instituted for the reception of a number of remarkable armoured Fishes of uncertain relationships which flourished in Europe during the Devonian and Old Red Sandstone periods, and in North America from the Devonian to the Lower Carboniferous. The head (_e.g._ in _Coccosteus_)[633] is invested dorsally by a series of median and lateral symmetrically-disposed tuberculated plates (Fig. 323). Two of the lateral plates are notched for the orbits, and between them there is an interorbital plate which either has a pit on its inner surface or is perforated by an open funnel, as in _Dinichthys_, possibly for a parietal or a pineal organ. Some of the bones present some analogy, to say the least, to certain of the dermal bones of a typical Teleostome, apparently representing such elements as paired parietals and frontals, a dermal mesethmoid, and toothless premaxillae and maxillae (Fig. 324, A). As in the Antiarchi, the anterior portion of the trunk is also armoured, above by a dorsal shield, formed by median and lateral plates, and below by a similarly constructed ventral shield (Fig. 324, B). A huge joint connects the head and trunk shields: hence the term Arthrodira or "joint-neck." The rest of the body is naked.

Pectoral fins are unknown, but pelvic fins, each supported by a stout basal plate or basipterygium, and with traces of radials, are present. There is a small dorsal fin. Little is known of the primary cranium, but in the trunk and tail it is evident {536}that there are well-developed and partially calcified neural and haemal arches associated with a persistent notochord. It is possible that the skull is autostylic. Gill-arches are not known. A pair of plates (Fig. 324, A, _j_) at the postero-lateral angles of the cephalic shield may perhaps be opercula. The teeth are conical. Those in the upper jaw are supported by two pairs of plates, probably vomers and palatines. In the lower jaw there are two series of teeth, one in front near the symphysis, and the other behind, supported by a single bone in each ramus. There is a well-developed lateral line system, indicated by surface markings on the head and trunk shields.

FAM. 1. COCCOSTEIDAE.—_Coccosteus_ occurs in the Devonian of Europe and North America, and includes species of relatively small size, not exceeding half a metre in length. _C. decipiens_, the best known species, is a characteristic fossil in the Old Red Sandstone of Scotland. _Phlyctaenaspis_[634] is found in the Lower Devonian of Canada, England, and Poland. A larger Arthrodiran, with slender toothless jaws, _Homosteus_,[635] is met with in the Lower Old Red Sandstone of the North of Scotland, and in the Devonian of Germany and Russia. The Old World Arthrodira must yield, however, to those of the New World for variety in size and shape, and in the character of their dentition.[636] {537}Some of the North American genera (_e.g. Dinichthys_) probably attained a length of ten feet, or even, as in _Titanichthys_, a much greater size. Some are fusiform in shape, but _Mylostoma_ is flattened and Ray-like, and, judging from the dentition, their food and habits must have been equally varied. _Mylostoma_ has tritoral plates not unlike those of _Neoceratodus_ or _Chimaera_. In others the teeth are single, and conical or pointed; in _Titanichthys_ the front teeth in both jaws are beak-shaped structures. It is highly probable that _Titanichthys_, _Mylostoma_, and perhaps other genera, are types of distinct families.

The Arthrodira have been regarded as armoured Dipneusti, a view which is mainly based on their supposed autostylism and the nature of the dentition. But this autostylism has yet to be verified, and, if proved, the possibility that it may be a secondary feature, associated with the evolution of a peculiar dentition, must not be forgotten. Much more may be said for their claim to be regarded as a highly specialised race of primitive Teleostomi. Besides a well-developed lower jaw, bones comparable to the elements of a secondary upper jaw are known, and in a general way the disposition of the cranial roofing bones, and the arrangement of the endoskeletal elements of the pelvic fins, tend to conform to the normal Teleostome type. In fact, Dr. Traquair has expressed the opinion that the Arthrodira are Teleostomi and Actinopterygii.[637]

TELEOSTEI (SYSTEMATIC PART)

BY

G. A. BOULENGER, F.R.S., V.P.Z.S.

Of the British Museum (Natural History)

{541}CHAPTER XXI

TELEOSTEI: GENERAL CHARACTERS—MALACOPTERYGII—OSTARIOPHYSI

ORDER IV. TELEOSTEI.[638]

As stated above (p. 495), the Holostean Ganoids pass very gradually into the Teleosteans, the lower groups of which appear to have been directly derived from them. The precise definition of the Order Teleostei, as compared with the Ganoid Order Holostei, is a matter of some difficulty. The most important character appears to be the presence of an ossified supraoccipital bone.[639] Remnants of primitive characters, such as ganoid scales, fulcra, rudiments of a splenial bone, spiral valve to the intestine, multivalvular conus arteriosus, are still found in some lower Teleosteans, but no longer in that combination which serves to define the preceding order. Although _Albula_ is exceptional among all Teleosteans in having two transverse series of valves to the bulbus arteriosus instead of one, no Ganoid has fewer than three.

The first remains of Teleosteans appear scantily in the Upper Trias, and it is not before we reach the Upper Cretaceous that they assume preponderance over other Teleostomes; whilst in the Upper Eocene they have already attained a development and variety of types comparable to their present condition. Out of some 12,000 well-established species of Fishes known to exist at {542}the present day, about 11,500 belong to this order. The classification of such an array of forms is, of course, a matter of great difficulty, and gives scope for much difference of opinion among those who have attempted to grapple with the subject. It is now recognised that the study of the skeleton affords the safest guide to a natural arrangement of the families and higher divisions. Much has been done in this line by Cope, Gill, Sagemehl, A. S. Woodward, and Jordan and his pupils; but the osteology of many important types still remains unknown. For some years a large number of skeletons have been prepared in the British Museum with the object of settling open questions, and this material has enabled me to draw up a scheme of classification which, whatever its defects, and however provisional, I feel sure is on the whole an improvement on those hitherto proposed, and especially on that generally in use in this country. The latter was, to a great extent, based on physiological principles; the present aims at being phylogenetic. In its preparation I have derived great benefit from the labours of the authors quoted above, but have endeavoured in every instance to verify their statements on a larger osteological material than appears to have been available to them. I have also had the advantage of the criticism, on many points, of my young colleague, Mr. C. Tate Regan, who has himself endeavoured to settle some important questions of classification.[640]

The Order Teleostei is divided into thirteen sub-orders, the probable relations of which are expressed in the following diagram:—

11. Opisthomi. 13. Plectognathi. 12. Pediculati. –––+
| | | |
+––––––––––––––––––+––––––––––––––––––––+ |
| |
9. Anacanthini. 10. Acanthopterygii. 8. Percesoces. |
| | | |
+––––––––––––––––––+––––––––––––––––––––+ |––Teleostei.
| |
7. Catosteomi. 5. Haplomi. 6. Heteromi. |
| | | |
+––––––––––––––––––+––––––––––––––––––––+ |
| | |
| 4. Apodes. |
| 3. Symbranchii. |
| |
1. Malacopterygii. 2. Ostariophysi. |
| | –––+
+––––––––––––––––––––––+
|
Ganoidei Holostei.

{543}In the classification of Günther, which has been generally in use in this country for the last thirty years, the Teleosts were divided into six principal groups, of ordinal rank: I. Acanthopterygii; II. Acanthopterygii Pharyngognathi; III. Anacanthini; IV. Physostomi; V. Lophobranchii; VI. Plectognathi. Group I. corresponds to Sub-Order 6 (part), 7 (part), 8 (part), 10 (part), 11 and 12 of the present work; Group II. to Sub-Order 10 (part); Group III. to Sub-Order 9 and 10 (part); Group IV. to Sub-Order 1, 2, 3, 4, 5, 6 (part), and 8 (part); Group V. to Sub-Order 7 (part); and Group VI. to Sub-Order 13.

SUB-ORDER 1. MALACOPTERYGII.

Air-bladder, if present, communicating with the digestive tract by a duct. Opercle well developed. Pectoral arch suspended from the skull; mesocoracoid arch present.[641] Fins without spines, the ventrals abdominal, if present. Anterior vertebrae distinct, without Weberian ossicles.

This sub-order, which corresponds to the Isospondyli and Scyphophori of Cope and to a part of the Isospondyli of A. S. Woodward, embraces the most generalised of the Teleosts, and is intimately connected with the Ganoids by the fossil forms which are placed at the base of the series of families. The physostomous condition of the air-bladder, the connexion of the pectoral arch with the skull, the presence of the mesocoracoid arch, the backward position of the many-rayed ventral fins, the normal condition of the anterior vertebrae, the absence of true spines to the fins, and the separation of the supraoccipital bone from the frontals by the parietals, are primitive characters which among the Teleosts occur combined in some families of this suborder only. The mesocoracoid arch is retained by the Ostariophysi, which differ in the remarkably modified condition of the anterior vertebrae, but it disappears in all other Teleosts, which gradually acquire a more forward position of the ventral fins and a reduction in the number of their rays, develop spines in the vertical fins, and lose the communication of the air-bladder with the outside.

The Malacopterygii may be divided into twenty-one families, the characters of which are contrasted in the following synopsis:—

I. Fins fringed with fulcra, or scales coated with ganoin; {544}
notochord
usually continuous through the vertebrae.

Vertebral centra not more than rings; fins with fulcra; scales
rhombic, united by peg-and-socket joints 1. _Pholidophoridae_.†

Vertebral centra not more than rings; fins with fulcra; scales
cycloid 2. _Archaeomaenidae_.†

Vertebral centra complete or with minute perforation; fins with
fulcra; scales cycloid 3. _Oligopleuridae_.†

Vertebral centra nearly complete, but with perforation; no fulcra;
scales cycloid 4. _Leptolepididae_.†

II. Fins without fulcra; scales without ganoin; vertebral centra
complete.

A. Supraoccipital separated from the frontals by the parietals or
upper surface of skull; no adipose fin.

1. Ventral fins with 10 to 16 rays.

An intergular bone; parasphenoid narrow 5. _Elopidae_.

No intergular bone; parasphenoid very broad 6. _Albulidae_.

2. Ventrals with not more than 7 rays.

a. Supratemporal very large, plate-like.

Praemaxillary single, its posterior extremity free from the
maxillary; symplectic absent; basis cranii simple
7. _Mormyridae_.

Praemaxillary paired, its posterior extremity firmly attached
to the maxillary; symplectic present; basis cranii double
8. _Hyodontidae_.

b. Supratemporal small; maxillary firmly attached to posterior
extremity of praemaxillary.

Praemaxillary paired; a large hole on each side of the skull,
between the post-frontal and the squamosal; basis cranii
double; suboperculum absent; ribs sessile
9. _Notopteridae_.

Praemaxillary paired; basis cranii simple; suboperculum reduced;
ribs inserted on parapophyses 10. _Osteoglossidae_.

Praemaxillary single; basis cranii simple; suboperculum and
interoperculum absent; ribs inserted on parapophyses
11. _Pantodontidae_.

c. Supratemporal small; maxillary movable; ribs sessile; ventral
fins below the pectorals 12. _Ctenothrissidae_.†

B. Supraoccipital separating parietals, or adipose fin present.

1. Interoperculum enormous; symplectic absent; basis cranii simple
13. _Phractolaemidae_.

2. Interoperculum normal; symplectic present; basis cranii double.

a. Teeth in sockets; maxillary firmly attached to praemaxillary.
Symplectic exposed 14. _Saurodontidae_.†

b. Teeth not in sockets.

Symplectic concealed between the quadrate and the hyomandibular
15. _Chirocentridae_.

Postclavicle on outer side of clavicle; no adipose fin
16. _Clupeidae_.

Postclavicle on inner side of clavicle; an adipose dorsal fin
17. _Salmonidae_.

Postclavicle absent; no adipose fin 18. _Alepocephalidae_.

3. Interoperculum normal; basis cranii simple. {545}

Maxillary large, toothed; praecaudal vertebrae without well-marked
parapophyses; scales cycloid or absent; adipose dorsal fin
present or absent 19. _Stomiatidae_.

Mouth small, toothless; vertebrae with strong parapophyses; head
and body covered with spiny scales 20. _Gonorhynchidae_.

Mouth small, toothless; no symplectic; head and body naked
21. _Cromeriidae_.

† This sign indicates that the group is represented by fossil forms only.

FAM. 1. PHOLIDOPHORIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter large and loosely attached; teeth small and conical. Parietal bones separating the supraoccipital from the frontals; opercular bones well developed. Vertebral centra never advanced beyond the annular stage; ribs delicate; no fused or expanded haemal arches at the base of the tail; no epipleurals or epineurals. Fin-fulcra present, but usually small; dorsal and anal fins small, the former above or behind the ventral fins, which are small or may be absent. Scales ganoid, rhombic, those on the flanks united by peg-and-socket joints.

This family, which appears to me to be related to the Dapediidae, is provisionally placed here by A. S. Woodward on account of its resemblance to the Leptolepididae, but it is not yet quite clear that the mandible was destitute of splenial and coronoid elements, while the bones at the base of the pectoral fin have not hitherto been observed. The principal genera are _Pholidophorus_, ranging from the Upper Trias to the Purbeck; _Thoracopterus_, from the Upper Trias; and _Pleuropholis_, from the Upper Jurassic. The species of _Pholidophorus_ are very numerous in the Jurassic period, and Woodward has observed that the scales of the later species are more elaborately ornamented than those of earlier date.

FAM. 2. ARCHAEOMAENIDAE.—Distinguished from the preceding by the thin, cycloid scales. Conspicuous obtuse ridge-scales are present along the dorsal and ventral lines. _Archaeomenes_, from the Jurassic (?) of New South Wales.

FAM. 3. OLIGOPLEURIDAE.—Characters as in Pholidophoridae, but scales cycloid and vertebrae completely or nearly completely ossified.

_Oligopleurus_, from the Jurassic of England and France; _Oenoscopus_, from the Jurassic and Cretaceous of France, Germany, and Italy; and _Spathiurus_, from the Cretaceous of Mount Lebanon and Dalmatia.

{546}FAM. 4. LEPTOLEPIDIDAE.—Praemaxillaries very small; maxillaries large, loosely attached; teeth small and conical. Parietal bones separating the supraoccipital from the frontals; opercular bones well developed. Vertebral centra well ossified, but always pierced by the notochord; ribs delicate; epipleurals present; no fused or expanded haemal arches at the base of the caudal fin. Dorsal and anal fins small, the former above or behind the ventrals. Ventrals with 5 to 10 rays. Scales thin, cycloid and deeply imbricate, usually coated with ganoin in their exposed portion.

_Leptolepis_, with numerous species, from the Jurassic and Cretaceous of Europe and New South Wales; _Vidalia_, Jurassic of France; _Aethalion_, Jurassic of Bavaria; _Thrissops_, Jurassic and Cretaceous of Europe; and _Lycoptera_, Jurassic of Asia.

FAM. 5. ELOPIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed, and movably articulated above the former to the ethmoid. Parietal bones in contact behind the frontals; opercular bones well developed. Basis cranii double. A bony intergular or sublingual plate. Jaws, palatines, pterygoids, vomer, parasphenoid, glossohyal, and pharyngeals toothed. Ribs mostly sessile, inserted very low down, behind parapophyses; epineurals similar to the ribs, but directed upwards. Pectorals low down, folding like the ventrals. Post-temporal forked, the upper branch attached to the epiotic, the lower to the opisthotic; post-clavicle small; scapular foramen in the scapula; pterygials well developed, three in contact with coracoid. Ventrals with 10 to 16 rays. Branchiostegal rays very numerous (over 20). Air-bladder large.

{547}This family is abundantly represented in Cretaceous times by the genera _Osmeroides_ and _Elopopsis_, and from the Lower Eocene to the present day by _Elops_ and _Megalops_. _Elops saurus_ is a handsome elongate silvery Fish, found in all the warm and tropical seas; the young are ribbon-shaped like those of _Albula_. A second species, _E. lacerta_, is from the West Coast of Africa, entering rivers. _Megalops_, distinguished by larger scales, the absence of pseudobranchiae, and the curious prolongation of the last ray of the dorsal fin, includes the well-known Tarpon _M. atlanticus_, and the Indian _M. cyprinoides_. The Tarpon occurs from the south-eastern coasts of North America and the West Indies to Brazil, and reaches a length of 6 feet and a weight of 110 lbs. It often leaps out of the water, after the manner of Grey Mullets, and its chase when hooked affords good sport, the landing of so active a giant being attended with great difficulties. Its remarkably large scales, over two inches in diameter, are much prized for fancy work in the Florida curiosity shops.

FAM. 6. ALBULIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter movably articulated above the former to the ethmoid. Parietal bones separating the supraoccipital from the frontals; suboperculum large; interoperculum small and entirely or nearly entirely hidden below the praeoperculum. Basis cranii double. Praemaxillaries, mandible, vomer, palatines, pterygoid, parasphenoid, glossohyal, and pharyngeals toothed. Ribs sessile, inserted behind and somewhat below small parapophyses, which are absent or merely indicated on the anterior vertebrae, and gradually increase in size towards the caudal region; these parapophyses, as well as the neural and haemal arches, are autogenous bones; epineurals, no epipleurals. {548}Pectorals low down, folding like the ventrals. Post-temporal trifid, the upper branch attached to the epiotic, the median to the squamosal, the lower to the opisthotic; post-clavicle large (formed of three pieces); scapular foramen between scapula and clavicle; pterygials well developed, two in contact with coracoid. Ventrals with 10 to 14 rays. Branchiostegal rays 6 to 14. Air-bladder large, not communicating with the ear.

Elongate fusiform Fishes, covered with large silvery scales forming regular longitudinal series; head naked; mouth rather small, with thick lips; gill-openings wide. Dorsal fin originating in front of ventrals; anal short; caudal well developed, forked.

The type of this family, _Albula_ or _Butirinus_, is remarkable among Teleosts in possessing a rudiment of a conus arteriosus to the heart, provided with two rows of valvules.[642] Its single species inhabits all the warm and tropical seas. Prof. Gilbert has ascertained that the young pass through a metamorphosis, analogous to that of the Eels. The "Leptocephalid" described as _Esunculus_ by Kaup is probably a larval _Albula_.

The deep-sea Japanese _Pterothrissus_ (_Bathythrissa_) must be placed in this family; its skeleton is very similar to that of _Albula_. It differs in the elongate dorsal fin, in the presence of small teeth on the maxillary bone, and in the small number of branchiostegal rays (6 instead of 12 to 14).

{549}_Albula_ is represented in the Eocene (London Clay and Bruxellian); and the Cretaceous _Istieus_ and _Anogmius_ are believed to be possibly related to _Pterothrissus_. Four Cretaceous types (_Plethodus_, _Thryptodus_, _Syntegmodus_, and _Ancylostylus_) are referred with doubt to the Albulidae.

FAM. 7. MORMYRIDAE.—Margin of the upper jaw formed by the single praemaxillary and the maxillaries, the latter articulated above the former to the ethmoid. Parietal bones separating the supraoccipital from the frontals; a large hole on each side of the skull, between the squamosal, the epiotic, and the opisthotic, covered by a large, thin, bony plate (the supratemporal), which may extend over a part of the parietal; symplectic absent; suboperculum small and hidden under the operculum, or absent; interoperculum well developed. Basis cranii simple. No pharyngeal teeth. Opercular bones hidden under the skin; gill-clefts narrow. Anterior ribs sessile; epineurals, no epipleurals. Pectorals directed upwards. Ventrals with 6 or 7 rays. Air-bladder communicating with the ear.

Curious-looking Fishes, very variable in the form of the head and body and in the extent of the fins. Mouth often very small; teeth in jaws usually few; teeth usually present on the parasphenoid, working against a similar patch on the glossohyal; eye covered over by skin, sometimes very indistinct; scales small, cycloid; branchiostegal rays 4 to 8. The dorsal and anal fins may be nearly equally developed (_Genyomyrus_, _Gnathonemus_); or the former (_Mormyrus_) or the latter (_Hyperopisus_) are several times the longer. _Gymnarchus_, Eel-shaped, apodal, and deprived of the caudal fin, lacks the anal fin, the dorsal extending over the whole extent of the body. Some species of _Mormyrops_ show how a form {550}like _Gymnarchus_ may have been evolved out of a more typically-formed Fish. Nothing is more striking than the variation in shape of the snout within one and the same genus, and the names given to some of the species (_ovis_, _caballus_, _elephas_, _tamandua_, _numenius_, _ibis_) are suggestive of resemblances with the heads of various animals.

The Mormyrids are highly remarkable for the enormous development of the brain, the weight of which equals 1/52 to 1/82 of the total, a thing unparalleled among lower Vertebrates; and for the problematic organ which surmounts it; also as being among the few Fishes in which an electric organ has been discovered. The organ, situated on each side of the caudal region, is derived from the muscular system and is of feeble power, as ascertained by Babuchin and by Fritsch; it was long considered as "pseudo-electric." The natural affinities of this family appear to be with the Albulidae, and there is nothing to justify the term "Nilhechte" (Nile-pike) which has been bestowed on them by German {551}authors. Ninety-three species are known from the fresh waters of Africa north of the Tropic of Capricorn, and may be referred to two sub-families and ten genera[643]:—

(i.) MORMYRINAE, with teeth on the parasphenoid and tongue, with ventral, anal, and caudal fins, and a simple air-bladder; vertebrae 37 to 64; peculiar (Gemmingerian) linear bones, without known homologues, along each side of the tail, above and beneath the electric organ; scapular foramen in the scapula, or between the scapula and the coracoid. _Mormyrops, Petrocephalus, Isichthys, Marcusenius, Stomatorhinus, Myomyrus, Gnathonemus, Genyomyrus, Mormyrus_.

(ii.) GYMNARCHINAE, without teeth on the parasphenoid and tongue, without ventral, anal, or caudal fins, and with a cellular air-bladder; vertebrae about 120; Gemmingerian bones absent; scapular foramen in the coracoid. _Gymnarchus_.

Fossil Mormyrids are unknown.

Venerated by the ancient Egyptians, the Mormyrs of the Nile are frequently represented on hieroglyphics and mural paintings as well as in bronze models. Very little is known of the habits of these Fishes. Prof. G. Fritsch, of Berlin, during his stay in Egypt for the purpose of experimenting on electric Fishes, observed that they perish very rapidly when removed from the river, and he had the greatest difficulty in keeping some alive in an aquarium for two or three days. The species with comparatively large mouths (_Mormyrops_, _Gymnarchus_) feed principally on fishes and crustaceans, the others on tiny animals and vegetable and more or less decomposed matter. Delhez, on the Congo, found that many are attracted to the borders of the river in the neighbourhood of human dwellings, where they feed on the refuse thrown into the water. It is probable that the species with a rostrum use it to procure small prey hidden between stones or buried in the mud, and that the fleshy mental appendage with which many are provided is a tactile organ compensating the imperfection of the vision in the search for food. A small Mormyrid from the Congo (_Stomatorhinus microps_) has the eyes so much reduced and the skin so feebly pigmented as to convey the impression of a cave Fish. Until quite recently, absolutely nothing was known {552}of the breeding habits and development in this important family. To the late J. S. Budgett we owe some very interesting observations made in the Gambia on _Gymnarchus niloticus_.[644] The Fish makes a floating nest, emerging on three sides, over which the male keeps a fierce watch; the recently-hatched larvae are remarkable for the enormous size of the yolk-sac, which hangs down, acting as a sort of anchor, and for the presence of long external branchial filaments, as in Selachian embryos. The Fish propels itself through the water entirely by the action of its dorsal fin, forwards and backwards with equal facility; when swimming rapidly backwards, it may be seen to use the end of its tail as a feeler to guide the way. Budgett has also identified, with some doubt, the eggs of _Hyperopisus bebe_, out of which emerged embryos not unlike those of some tailless Batrachians, which hung suspended to rootlets of grass in swamps by means of threads of viscid mucus secreted from glands on the top of the head.

FAM. 8. HYODONTIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly united to the end of the former. Parietal bones separating the supraoccipital from the frontals; a large hole on each side of the skull, between the parietal, the squamosal, and the epiotic (paroccipital), closed by a large, thin, bony plate (the supratemporal), which extends over the greater part of the parietal; suboperculum and interoperculum small, the latter partly hidden below the praeoperculum. Basis cranii double. Jaws, palatines, pterygoids, vomer, parasphenoid, and glossohyal toothed; no pharyngeal teeth. Ribs sessile, inserted above and behind well-developed parapophyses; epineurals, no epipleurals. {553}Pectorals low down, folding like the ventrals. Post-temporal forked; the upper branch attached to the epiotic, the lower to the squamosal; no post-clavicle; coracoids forming together a ventral keel; scapular foramen between scapula and clavicle; pterygials well developed, three in contact with coracoid. Ventrals with 7 rays. Branchiostegal rays in moderate number (8 to 10). Air-bladder communicating with the ear. No oviducts, the eggs falling into the abdominal cavity before exclusion.

Elongate, compressed, silvery Fishes, covered with moderate-sized cycloid scales; head naked; mouth large, with strong dentition; gill-openings wide; dorsal fin short, posterior to the ventrals; anal rather elongate; caudal well developed, forked.

A single genus (_Hyodon_) with three species (Moon-Eyes of the Americans), all reaching the length of about a foot, inhabiting the fresh waters of North America east of the Rocky Mountains.

{554}FAM. 9. NOTOPTERIDAE. The Fishes which form this family may be regarded as an eccentric modification of a type very similar to the preceding, with which they agree in most osteological features as well as in the dentition, in the connexion between the air-bladder and the ear, and in the absence of oviducts. They differ in the absence of the lid-like supratemporal, the hole which it covers in _Hyodon_ being here bordered by the post-frontal and the squamosal (fused with the opisthotic), sometimes also by the epiotic, in the absence of the suboperculum, in the absence or incomplete ossification of the upper branch of the post-temporal (the lower articulating with the opisthotic), and in the presence of accessory bones (named adpleurals) attached to or fused with the distal extremity of the anterior ribs, which they prolong to the mid-ventral line, where they are embraced by dermal ossifications forming a doubly serrated crest.

The bones of the head are cavernous, the mouth is large; the anterior nostril is produced into a tentacle. The body is very strongly compressed, with very short precaudal region, attenuate behind; the ventral fins are much reduced or absent; the dorsal is short or absent, {555}and the anal is much elongate and confluent with the caudal, which may be regarded as aborted. The scapular foramen is entirely in the scapula. The air-bladder is very large, with several divisions, forked in front and behind, and prolonged along each side of the caudal region; its extraordinary condition has been described by Bridge.[645]

These Fishes live in marshes and lakes, fresh-water or brackish, and feed on worms and insects. Nothing is known of their breeding habits and development.

Two genera: _Notopterus_, with a dorsal fin and 6 to 9 branchiostegal rays—three species from India, Burma, and the Malay region, and one from West Africa; _Xenomystus_, without dorsal fin and with only 3 branchiostegal rays, the unique species inhabiting the White Nile and West Africa. Remains of _Notopterus_ have been found in the marl slates (Tertiary) of Padang, Sumatra. The largest species, the Indian _N. chitala_, attains 4 feet in length; its flesh is said to be uncommonly rich and well flavoured, but a strong prejudice exists against it, owing to the Fish being supposed to live on human carcases.

FAM. 10. OSTEOGLOSSIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly attached to the end of the former. Parietal bones separating the supraoccipital from the frontals; suboperculum much reduced, and entirely or partially concealed under the praeoperculum. Basis cranii simple. Teeth in jaws, and on pterygoid and hyoid bones; no pharyngeal teeth. Head scaleless, the thin skin confluent with the bones; body covered with large bony scales, composed of pieces like mosaic. Ribs inserted on the strong parapophyses; epineurals, no epipleurals. Pectoral fins low down. Post-temporal forked, the upper branch attached to the epiotic, the lower to the squamosal; post-clavicle present; scapular foramen in scapula; pterygials well developed, only one in contact with coracoid. Dorsal and anal fins originating behind the ventrals; latter with 5 or 6 rays. No oviducts, the eggs falling into the abdominal cavity before exclusion (at least in _Heterotis_, as observed by Budgett).

This family is represented at the present day by five species, referred to four genera; thus characterised:—

{556}

{557}_Scleropages_.—Mouth large; vomer, palatines, pterygoids, and glossohyal toothed; mandibular barbels; branchiostegal rays 15 to 17; body compressed, with trenchant abdomen; coracoids forming a ventral keel; dorsal fin short; ventral fins nearly equally distant from end of snout and caudal fin; vertebrae 29 to 31 + 30; air-bladder not cellular. One species from the northern parts of Australia, and one from Sumatra, Banka, and Borneo.

_Osteoglossum_.—Mouth large; vomer, palatines, pterygoids, and glossohyal toothed; mandibular barbels; branchiostegal rays 10; body compressed, with trenchant abdomen; coracoids forming a ventral keel; dorsal fin long; ventral fins nearly twice as far from the caudal as from the end of the snout; vertebrae 28 + 59; air-bladder not cellular.—South America (Guianas, Brazil).

_Arapaima_.—Mouth rather large; vomer, palatines, pterygoids, and glossohyal toothed; branchiostegal rays 16; belly rounded; dorsal fin rather long; ventral fins equidistant from head and caudal fin; vertebrae 36 to 38 + 41 to 42; air-bladder cellular.—South America (Guianas, Brazil).

_Heterotis_.—Mouth moderate; branchiostegal rays 7; belly rounded; dorsal fin rather long; ventral fins nearer end of snout than caudal fin; vertebrae 27 + 42 to 43; air-bladder cellular; fourth branchial arch with an accessory breathing-organ. Africa (Nile, Senegal, Gambia, Niger).

_Dapedoglossus_, from the Eocene of Wyoming, appears to be nearest to _Scleropages_, and _Brychaetus_, from the Eocene (London Clay) of Sheppey, Kent, to _Arapaima_, so far as the state of preservation of these fossils enables us to form an opinion.

Dr. Günther has directed attention to the remarkable {558}coincidence of the geographical distribution of this family and the Dipneusti, although, however, the latter are not known to be represented in the Malay Archipelago. "Not only," he adds, "are the corresponding species found within the same region, but also in the same river systems; and although such a connexion may and must be partly due to a similarity of habit, yet the identity of this singular distribution is so striking that it can only be accounted for by assuming that the Osteoglossidae are one of the earliest Teleosteous types which have been contemporaries of and have accompanied the present Dipnoi since or even before the beginning of the Tertiary epoch."

The Queensland species of _Scleropages_ (_S. leichardti_) is known to the settlers by the name of Barramunda, which has also been applied to _Neoceratodus_. _Arapaima gigas_ is one of the largest fresh-water Fishes known, exceeding a length of 15 feet and a weight of 400 pounds. Its flesh is much valued. Sir R. Schomburgh has observed that the mother protects the young, who, for some time after their birth, always swim in front of her. A similar observation has been made in the Gambia on _Heterotis niloticus_ by the late J. S. Budgett, who states that the Fish builds enormous nests in swamps, in about two feet of water; the walls of the nest are made of the stems of the grasses removed by the Fish from the centre; the floor is the swamp-bottom, and is made perfectly smooth and bare. The nest appears to be used for at most four or five days; the newly-hatched larvae are provided with long external gill-filaments of a blood-red colour.[646]

FAM. 11. PANTODONTIDAE.—The little West African Fish described by Peters as _Pantodon buchholzi_ is the unique representative of a family closely related to the Osteoglossidae, but distinguished by the very small, single praemaxillary and the absence of suboperculum and interoperculum. The pectoral fins are very large and are remarkable for the fleshy process to which the inner ray is adnate; the ventrals, formed of 7 rays, some of which are simple and prolonged into filaments, are placed more forward than in any other type of this sub-order, the Ctenothrissidae excepted, viz. immediately behind the pectorals. Teeth in the jaws and on the vomer, palatines, pterygoids, parasphenoid, {559}glossohyal, and pharyngeal bones. Mesocoracoid arch slender, strongly curved, and meeting its fellow on the median line; coracoids forming a ventral keel. Vertebrae few (16 + 14).

Observed by M. de Brazza to be a freshwater Flying-Fish.