Chapter XXXV: Palaeozoic Gymnospermous Seeds (2)

Impressions of _Codonospermum_ are described[899] from Commentry, from the Loire—the Gard district[900], and by Zeiller[901] from Blanzy. There is no decisive evidence as to the parent-plant, but some French authors[902] regard the frequent association of _Codonospermum_ with leaves of _Dolerophyllum_ as significant.

=Aetheotesta.= Brongniart.

_Aetheotesta elliptica_ Renault.

Brongniart instituted the genus _Aetheotesta_[903] for an incomplete seed (_A. subglobosa_) from Grand’ Croix, and Renault[904] subsequently founded the species _A. elliptica_ on much better material. The testa of the elliptical seed, 3 cm. long, consists of an outer region very thin on the flanks but highly developed at the apex and base which forms a sarcotesta characterised in the apical region by large radially disposed spaces, fig. 498, C, _s_; the sclerotesta, composed of harder tissue, is prolonged as an apical beak. There is a large pollen-chamber, _pc_, in which Renault found multicellular microspores (320μ–400μ). In the chalazal region the main vascular supply forms a cup-like investment, _v_, in the basal portion of the nucellus, and at a higher level this breaks up into several nucellar strands. Renault thinks that _Aetheotesta_ is the seed of _Dolerophyllum_, but there is no proof of any connexion. The presence of large spaces in the sarcotesta may be interpreted, as Renault suggests, as evidence of adaptation to dispersal by water.

=Eriotesta.= Brongniart.

Brongniart[905] instituted this genus[906] on an incomplete transverse section of a seed from Grand’ Croix, 8 mm. in diameter, which he called _Eriotesta velutina_, characterised by a ribbed and probably octagonal testa bearing numerous elongated hairs over the whole surface. The material is, however, too meagre to throw any light on the important features of the seed.

=Gaudrya.= Grand’Eury.

_Gaudrya trivalvis_ Grand’Eury.

The generic name _Gaudrya_[907] was proposed for two petrified seeds from the Gard coal-field briefly described as _G. trivalvis_, the type-species, and _G. lagenaria_. The testa of the former species shows signs of splitting along three equidistant lines; it consists of a sarcotesta enclosing an endotesta with six longitudinal ribs: Grand’Eury speaks of lacunae between the endotesta and nucellus which he regards as spaces in a tissue which made the seed buoyant and facilitated dispersal by water. It is not clear whether the nucellus and integument were originally connected or laterally free: the lacunae may be the remains of an inner flesh and not spaces in a spongy tissue. The genus is radiospermic and characterised by a long micropyle and a broad pollen-chamber. On the available evidence it is difficult to assign the specimens to their systematic position, but the genus is probably a member of the Trigonocarpales.

III. +Cardiocarpales.+

Platyspermic seeds for the most part belonging to Cordaitalean plants and agreeing in their plan of organisation, even more closely than the seeds of the Trigonocarpales, with those of recent Cycads. The nucellus is free laterally from the integument and there is a series of vascular bundles in the nucellus. The testa consists of an outer flesh, the sarcotesta, which may reach a considerable thickness, a shell or sclerotesta, and in some genera an endotesta. In seeds preserved as impressions the sarcotesta often gives them a winged appearance (_Samaropsis_). The pollen-chamber is relatively small, resembling in this respect the chamber in recent Cycads. A central prolongation of the prothallus-tissue in the form of a blunt column or ‘tent-pole’ is a characteristic feature; the same feature occurs in seeds of the Lagenostomales, but in the Cordaitales it resembles more nearly the ‘tent-pole,’ as it was called by Hirase, in recent Cycadean seeds and in _Ginkgo_. The presence of two vascular strands in the sarcotesta in the principal plane of the seeds is a character shared with the seeds of _Cycas_: the position and course of these bundles are useful characters for distinguishing different types within the group. The microspores are multicellular.

Genera. _Cardiocarpus_; _Cyclospermum_; _Cycadinocarpus_; _Rhabdospermum_; _Mitrospermum_; _Diplotesta_; _Leptocaryon_; _Taxospermum_; _Compsotesta_. These generic names are all used in the following pages for seeds known to possess certain anatomical features; there are also included in the Cardiocarpales the genera _Samaropsis_, _Cordaicarpus_, and _Rhabdocarpus_, but it is proposed to limit their use to specimens which furnish no anatomical data and cannot therefore be assigned with equal confidence to a section of seeds based on definite morphological characters. It is certain that some at least of the seeds described under these names would, if preserved as petrified specimens, be included in one or other of the genera named above.

There is ample proof that some of these seeds were borne on Cordaitean plants and that the group as a whole represents the seeds of the Cordaitales[908]. It is, however, certain that some Platyspermic seeds were produced by Pteridosperms. No little confusion has been caused by the employment of the same generic names for petrified seeds and for casts and impressions affording no evidence as to similarity in anatomical characters. With a view to avoid the risks necessarily entailed by following this practice it is suggested that a clearer distinction should be drawn between genera based primarily on structural features and form-genera. The following notes on the genera _Cardiocarpus_, _Cordaicarpus_, _Cyclocarpon_, _Cycadinocarpus_, _Jordania_, and _Samaropsis_, may serve to illustrate some of the difficulties connected with the terminology of Palaeozoic seeds.

_Cardiocarpus_. Brongniart[909] proposed the name _Cardiocarpon_ in 1828 for Upper Carboniferous seeds described as compressed lenticular, cordiform or reniform ‘fruits’ with an acute apex: in his later work[910] he recognised their true morphological nature and gave an account of some exceptionally well-preserved examples from Grand’ Croix. Brongniart in common with other authors believed _Cardiocarpus_ seeds to belong to Cordaitean plants, a view that in several cases is based on conclusive evidence. The specimen represented in fig. 501, D, illustrates the characteristic form of a cast of a _Cardiocarpus_ seed, and the sections shown in fig. 501, A and B, are from an identical or a very closely allied species. The generic characters are: (i) the presence of a narrow flattened border or wing surrounding a platyspermic nucule, (ii) the cordiform base and more or less pointed apex, (iii) the differentiation of the testa into a sarcotesta and sclerotesta free from the nucellus except at the base, (iv) the ‘tent-pole’ prolongation of the prothallus (fig. 510, A, _b_) and the presence of a fairly large pollen-chamber, _pc_, (v) the occurrence of two sets of vascular bundles, an inner nucellar series and two double vascular strands (fig. 500, A, _v_, B) which are given off from the main supply before it reaches the sclerotesta. The term _Cardiocarpus_ as used by Brongniart signifies a type of seed possessing both certain anatomical and external characters. The proposal is to restrict the generic appellation to seeds exhibiting definite structural features agreeing in essentials with _Cardiocarpus sclerotesta_ and _C. drupaceus_.

_Cordaicarpus_. This name was first employed by Geinitz[911] in the form _Cordaicarpon_, the type-species being _C. Cordai_ (fig. 502, C) from the Coal Measures of Germany, a seed referred by the author of the genus to _Cordaites principalis_ but, as Kidston has pointed out, there is evidence that this correlation may be incorrect: there is, however, no doubt as to its Cordaitean parentage. Specimens included in this genus agree closely with species of _Cardiocarpus_, but they are usually described as being distinguished by the absence of a flat border and by a more rounded and less cordate base. In the example of _Cordaicarpus Cordai_ shown in fig. 502, C, and in other species assigned by authors to this genus there is a narrow border and the form of the base is an inconstant character. As Kidston[912] and other authors point out, there are no definite and constant characters by which to distinguish _Cardiocarpus_ from _Cordaicarpus_ as regards the form of the seeds preserved as casts or impressions. A further account of _Cordaicarpus_ is given on a later page.

_Cordaispermum_. This designation was formerly adopted by Renault[913] for seeds having the form and anatomical features of _Cardiocarpus_ which there is good reason for attributing to _Cordaites_ or to some allied genus. In view of the fact that the majority of the seeds under consideration are undoubtedly Cordaitean there is no need to employ this additional generic name.

_Cyclocarpon_. Fiedler[914] instituted this term for seeds previously described by Berger as _Cardiocarpon emarginatum_ (fig. 502, B, now included in _Samaropsis_) and added a new species _Cyclocarpon nummularium_. Brongniart[915] subsequently described the structure of two species, _C. tenue_ and _C. nummulare_, which he referred to Fiedler’s genus, and Bertrand[916] has shown that these differ from the genus _Cardiocarpus_ in the recurrent course of the bundles given off from the chalazal strand as in the genus _Rhabdospermum_ (cf. fig. 501, E). There are no good grounds for retaining the designation _Cyclocarpon_ for casts and impressions, as the specimens so named are indistinguishable from impressions referred to _Cordaicarpus_. The generic name _Cyclocarpus_, retained by Bertrand only for _C. tenuis_ and _C. nummularis_ simply for anatomical reasons, is now altered to _Cyclospermum_ on the ground that the designation _Cyclocarpon_ has been used for impressions affording no information with regard to anatomical features.

_Cycadinocarpus_. Renault[917] transferred to this genus Brongniart’s species _Cardiocarpus augustodunensis_ on the ground that the vascular system exhibits in a greater degree than the other types included by Brongniart in _Cardiocarpus_ a resemblance to that in recent cycadean seeds. Bertrand[918] confirms Renault’s account and retains _Cycadinocarpus augustodunensis_ as a species worthy of generic distinction. A short account of this seed is given on a later page.

_Jordania_. This name was given by Fiedler[919] to compressed ovate-cordate seeds characterised by a broad membranous border bearing a superficial resemblance to the seeds of _Bignonia_. The type-species, _J. bignoniodes_ (fig. 502, I), from the Coal Measures of Saarbrücken has the form usually associated with the designation _Samaropsis_, and as the latter term is generally adopted there are no adequate reasons for the retention of _Jordania_. The name _Jordania_ has also been applied, by Schenk[920], to fossil Dicotyledonous wood and was previously used by Boissier[921].

_Samaropsis_. Goeppert[922] defined _Samaropsis_ as ‘Fructus samaroideus membranaceus, compressus, margine alatus, monospermus.’ The type-species, _S. ulmiformis_, from the Permian of Brenau, is a small seed with a broad wing or border, but a better example of _Samaropsis_ is figured by Goeppert as the wing of an insect[923]. Examples of the genus are shown in figs. 502, A–H; 503; 504. Seeds included in _Samaropsis_ differ from those referred to _Cordaicarpus_ in the presence of a broader and more clearly defined border which in some cases, as in the genus _Mitrospermum_ (fig. 494, K, L), undoubtedly represents a lateral wing-like extension of the sarcotesta. In some instances the wing may be a tangentially expanded integument comparable with the perianth of _Welwitschia_, and in some Jurassic seeds referred by Heer[924] to _Samaropsis_ the lateral appendages are probably true wings. It is advisable to restrict the designation _Samaropsis_ to Palaeozoic seeds. Nucules deprived of the broad border would be referred to _Cordaicarpus_ as usually employed for impressions. The generic name _Samaropsis_ serves a useful purpose as a distinctive term for platyspermic seeds preserved as casts or impressions characterised by the possession of a wide border or wing broader than in typical examples of _Cordaicarpus_. The specimen represented in fig. 499 affords a good illustration of the difference between _Samaropsis_ and _Cordaicarpus_. In this specimen the border clearly consists of two portions, an inner narrower border (black in the drawing) and an outer more delicate portion; the former is the impression of the sclerotesta and the outer represents the fleshy sarcotesta which in the living seed may have formed a wing. If, as often happens, the seed were preserved with the narrow border only it would be assigned to _Cordaicarpus_, many species of which are undoubtedly incomplete _Samaropsis_ seeds.

The seeds described by Lindley and Hutton as _Cardiocarpon acutum_ (fig. 444, p. 171) have been made by Arber[925] the type of a new genus _Cornucarpus_, the distinguishing feature being the triangular form and the apical horns of the wing. The seeds figured by Arber[926] from the Kent coalfield as _Cornucarpus acutus_ are, however, not identical with the type of Lindley and Hutton, which has the characters of _Samaropsis_. _Samaropsis_ is widely distributed in Permo-Carboniferous rocks in Europe and North America and is recorded also from India[927] (fig. 504), China[928], South Africa[929] (fig. 503), South America[930] (fig. 502, F, G) and Australia[931]. Some seeds of this form were certainly borne on Cordaitean plants (cf. fig. 480, A), but seeds of similar type have been found in organic connexion with the foliage of Pteridosperms (figs. 442, 445, pp. 167, 172). The Permian ‘cone-scales’ bearing seeds described by Geinitz as _Cardiocarpon triangulare_[932], represented by well preserved impressions in the Dresden Museum, appear to be of the _Samaropsis_ type: the same author referred some _Samaropsis_ seeds to the Conifer _Walchia_, but Weiss[933] dissents from this correlation as the seeds often occur in beds in which _Walchia_ is not represented. Renault states that the seeds of the fertile shoot described by him as _Cycadospadix Milleryensis_[934] from Autun [= _Strobilites Milleryensis_ (Ren.)] closely resemble _Samaropsis fluitans_ Daws. as figured by Weiss. The suggestion by White[935] that _Samaropsis_ seeds were borne on fertile leaves of _Gangamopteris_ adds a further difficulty to the use of the generic characters of _Samaropsis_ as criteria of systematic position. The Permian seeds figured by Goeppert[936] as _Oreodoxites Martianus_ are possibly specimens of _Samaropsis_.

The designation _Samaropsis_, though usually restricted to Palaeozoic species, is applied by some authors to ‘winged’ seeds from Mesozoic strata; but as some of the Jurassic seeds[937] so named appear to have true wings like those of some recent Conifers it is advisable to adhere to the more limited use of the name.

It is safe to assert that many _Samaropsis_ seeds agreed generally in structure with Cordaitean seeds such as the petrified examples described by Brongniart as _Cardiocarpus_. The species _Mitrospermum compressum_[938] is an example of a petrified seed having the external features of _Samaropsis_.

=Cardiocarpus.=

This generic title I propose to restrict to petrified seeds exhibiting the characters described by Brongniart[939] and more recently by Bertrand[940] in _C. sclerotesta_ and _C. drupaceus_. In general organisation seeds of this generic type agree with those of recent Cycads and with the seed of _Ginkgo biloba_, but there are certain distinguishing features. An important character is afforded by the course and place of origin of the lower vascular strands from the main supply at the base of the seed. The outer vascular system consists of two bundles given off from the main strand, before it reaches the sclerotesta, which pass up the sarcotesta (fig. 500, B). In _Rhabdospermum_, on the other hand, the corresponding bundles arise at a higher level and form recurrent strands which penetrate the sclerotesta before passing up the fleshy part of the integument (cf. fig. 501, E).

_Cardiocarpus sclerotesta_ Brongniart. The testa is differentiated into an inner shell and an outer sarcotesta (fig. 501, A; the sclerotesta is shown in black); there is a well developed pollen-chamber (_pc_) and below this the prothallus-tissue is prolonged as a blunt and short tent-pole, _b_, as in _Gingko_ and in several fossil seeds. On each side of the apical tent-pole the slightly shrunken prothallus shows two small archegonia, _a_, which in the relatively small size and spherical form of the egg-cells resemble those of _Ginkgo_. In transverse section (fig. 501, B) the seed is bi-convex and at each end of the major axis the sclerotesta forms a small keel. There are two sets of vascular bundles concerned in the supply of material to the ovule; a lower pair of bundles given off from the central strand in the sarcotesta (fig. 500, B) which pass to the apical region in the inner tissues of the sarcotesta in the principal plane (fig. 500, A, _v_), and an inner set of bundles that pass up the peripheral tissue of the nucellus.

The species described by Brongniart as _Cardiocarpus (Cyclocarpus) tenuis_ and _C. nummularis_ have been removed by Bertrand[941] from _Cardiocarpus_ on the ground that the integumental bundles pursue a course like that in _Rhabdospermum_; it is now referred to the new genus _Cyclospermum_[942].

=Cyclospermum.= Gen. nov. (= _Cyclocarpus_ Bertrand).

As stated on a previous page Bertrand[943] re-establishes the generic name _Cyclocarpus_, founded on impressions without reference to anatomical characters, for two petrified seeds from St Étienne described by Brongniart as _Cardiocarpus tenuis_ and _Cyclocarpus nummularis_[944]. These types differ from _Rhabdospermum_ in the absence of an apical snout but agree with that genus in the steeply descending course of the vascular strands in the basal region of the seed. As stated on a previous page, the name _Cyclospermum_ is proposed as a substitute for _Cyclocarpus_ because of the employment of the latter term for impressions.

=Cycadinocarpus.= Schimper[945].

_Cycadinocarpus augustudunensis_ (Brongniart[946]). In the possession of two sets of vascular bundles this type agrees with _Cardiocarpus_, but the more internal strands pass up on the inner face of the sclerotesta without penetrating into the nucellus, a feature in which _Cycadinocarpus_ agrees with the majority of recent cycadean seeds: the outer bundles are given off from the main supply after it has entered the sclerotesta and not before as in _Cardiocarpus_; they follow an oblique course in the sclerotesta and emerge into the sarcotesta at the shoulders of the basal curve of the seed. As in _Cardiocarpus_ and _Rhabdospermum_ the two outer bundles lie in the principal plane of the seed. There is a pollen-chamber at the apex of the nucellus and the latter tissue is prolonged as a tent-pole which engages with the micropyle. In the absence of data as to the course of the vascular bundles in the chalazal region it would not be possible to distinguish between this genus and _Cardiocarpus_.

=Rhabdocarpus= Berger and =Rhabdospermum= gen. nov.

It is proposed to restrict the name _Rhabdocarpus_[947] to impressions and casts of seeds of the type represented by _R. tunicatus_ as figured by Berger[948] and reproduced in fig. 506, K, the term _Rhabdospermum_ being applied to seeds of similar form in which are shown certain distinguishing anatomical features. _Rhabdocarpus tunicatus_ Berger is a species founded on a specimen from the Coal Measures of Silesia characterised by an outer carbonised testa prolonged apically as a blunt snout and, as seen in fig. 506, K, covering an apparently ribbed nucule, but the ‘ribs’ are due to the presence of fibrous strands and are not ribs in the ordinary sense. The outer tissue shows numerous longitudinal striations due presumably to the presence of fibrous elements in the sarcotesta like those shown in the petrified seed represented in fig. 501, C. The genus is defined by Berger as follows: ‘Semina ovata vel elliptico-oblonga secundum longitudinem parallele nervosa vel tenuissime striata, putamine (interdum deficiente) instructa.’ As used by Berger and many other authors _Rhabdocarpus_ includes a miscellaneous collection of seeds often differing widely from the type-species. Many of the examples correctly referred to Berger’s genus are platyspermic though a bilateral symmetry is by no means always clear. Renault and Zeiller[949] in their definition of _Rhabdocarpus_ include bilateral symmetry as a characteristic feature and speak of the seeds as oblong or oval with a pointed or truncate apex and a rounded base. Impressions of _Rhabdocarpus_ differ from those of _Cardiocarpus_ or _Cordaicarpus_ in their more elongate form, always longer than broad, and in the absence of a basal sinus. The seeds found attached to _Neuropteris_ pinnae and, in external features, agreeing with many specimens included in Berger’s genus, have been transferred by P. Bertrand[950] and Arber[951] to a new genus _Neurospermum_[952]. Arber[953] in his recent revision of British seeds proposes to restrict the name _Rhabdocarpus_ to platyspermic seeds having a ‘large unsymmetrical nucule enclosed in a large unsymmetrical wing or sarcotesta,’ that is to forms symmetrical in one plane. In this category he includes _Rhabdocarpus tunicatus_ Berg. (fig. 506, K) and _R. subtunicatus_[954] Grand’Eury, but it is not clear on what grounds Berger’s species is spoken of as symmetrical in only one plane: in the species _R. Lilleanus_ Arb.[955] the symmetry is hardly sufficiently well defined to rank as a generic character. In the case of the _Neuropteris_ seeds the apical snout is slightly curved, thus giving them an unsymmetrical appearance (cf. fig. 422, p. 114). The Carboniferous and Permian seeds usually referred to _Rhabdocarpus_ are transferred by Arber to his genus _Platyspermum_[956], a designation for which it is proposed to substitute Nathorst’s genus _Holcospermum_[957]. In seeds preserved as more or less flattened impressions it is practically impossible in many cases accurately to determine the symmetry: as fig. 506, A, shows, casts indistinguishable from some examples of _Platyspermum_ are radially symmetrical. Brongniart[958] extended the original definition of _Rhabdocarpus_ to include certain anatomical characters, and these have been more fully defined by Bertrand[959]. It is for seeds showing these anatomical features that the name _Rhabdospermum_ is now proposed. This course is followed on the ground that it is advisable to avoid confusion between petrified specimens and impressions which in spite of superficial resemblance may not be closely related. In some cases it is practically certain that an impression of the _Rhabdocarpus_ type is generically identical with a seed of similar form showing the anatomical structure of _Rhabdospermum_, but unless identity is established a distinct terminology is preferable. The use of the generic name _Rhabdospermum_ carries with it an implication of platyspermy, but under _Rhabdocarpus_ may be included seeds which are radiospermic and platyspermic. Some seeds agreeing with _Rhabdospermum_ are referred by Grand’Eury[960] to _Poroxylon_, and it is probable that _Rhabdospermum_ like _Cardiocarpus_ is a Cordaitean seed. On the other hand _Rhabdocarpus_ may well include species, apart from those transferred to _Neurospermum_, that belong to Pteridosperms. A species, _Rhabdocarpus Oliveri_, recently described by Kidston[961] from the Staffordshire coalfield is an example of a radiospermic seed which may be assigned to a Pteridosperm. The type-specimen is an ovate seed 4 cm. long and 2 cm. broad agreeing in form and surface-features with _Rhabdocarpus_ as already defined, but the evidence it affords of internal structure is insufficient to determine its position with regard to genera founded on anatomical characters. Other examples of _Rhabdocarpus_ are described by Lesquereux[962] and White[963] from American Coal Measures, by Grand’Eury[964] from the Loire, by Renault[965] from Autun, and by many other authors.

=Rhabdospermum.= Gen. nov.

The platyspermic seeds included in this genus agree in size and form with impressions assigned to _Rhabdocarpus_ and as regards the main features conform anatomically to _Cardiocarpus_; they were probably borne on Cordaitean plants. Fig. 501, C, represents a longitudinal section of the species _Rhabdospermum cyclocaryon_ described by Brongniart as _Rhabdocarpus cyclocaryon_: the sarcotesta is particularly well developed in the apical region; at the apex a portion of the micropyle is seen at _m_ and near the nucellus are pieces of the sclerotesta shown in black. The presence of anastomosing fibres near the surface is a characteristic feature: these, as Bertrand points out, do not form a hypodermal tissue in the strict sense as they may be separated by some of the thin-walled parenchyma of the sarcotesta from the epidermis. The sclerotesta is only partially preserved but the inner portion forms a dark line enclosing the nucellus, the superficial tissue of which is separated from the shrunken prothallus represented by the almost spherical dotted region: the remains of an archegonium are seen at _a_ (fig. 501, C) and the characteristic tent-pole apex of the prothallus is shown at _b_. While in shape and in the general plan of organisation _Rhabdospermum_ agrees with _Cardiocarpus_, the vascular system in the chalazal region constitutes a distinguishing feature. In _Rhabdospermum_ the main vascular strand passes through the sclerotesta, _e_, _e′_, fig. 501, E, before giving off two bundles which bend back (‘faisceaux récurrents’), traverse the shell, and then pass up the sarcotesta in correspondence with the feebly developed lateral keels as far as the micropyle, while in _Cardiocarpus_ (fig. 500, B) the bundles are given off before the main strand reaches the sclerotesta. Similar recurrent bundles occur also in _Mitrospermum_ (fig. 494, K)[967].

=Mitrospermum.= A. Arber.

_Mitrospermum compressum_ (Williamson). Mrs Arber[968] proposed the name _Mitrospermum_[969], suggested by the peculiar form of the seed-base, as a substitute for _Cardiocarpon_ for Williamson’s species _C. compressum_[970] from the Lower Coal Measures of Lancashire. The seed is platyspermic and there is some evidence that it split into two valves along the principal plane (the longer axis of the section, fig. 494, L). The diagrammatic and partially restored longitudinal section reproduced in fig. 494, K, shows the main features: a sarcotesta, _sa_, covers the surface of the testa as a thin layer except at the edges of the flattened sides where it forms a wing-like border; preserved as an impression the seed would be assigned to _Samaropsis_. The sclerotesta, _sc_, has a pointed apex which surrounds the lower third of the micropyle and a broad base perforated by the chalazal vascular strand. There was probably a narrow inner flesh as in _Trigonocarpus_ and recent Cycadean seeds (fig. 494, K, _cf_). The nucellus was free from the integument except at the base, as in _Trigonocarpus_ and _Stephanospermum_ (fig. 494, K, _n_): internal to the shrivelled remains of the inner flesh there was a nucellar tapetum surrounding the megaspore. Details as to the pollen-chamber are lacking though there are indications that it resembled that of some species of Cordaitean seeds. The main vascular supply passes through the sclerotesta and then forms a low cushion of short reticulate elements below the base of the nucellus from which two bundles are given off (fig. 494, K, _v_) in the principal plane. The course of the bundles which pierce the sclerotesta led Mrs Arber to remove this seed from _Cardiocarpus_, as recently defined by Bertrand[971], since in that genus the integumental bundles have their origin below the sclerotesta. In the course of the vascular bundles _Mitrospermum_ is intermediate between _Rhabdospermum_ and _Taxospermum_.

This genus is founded on a detached seed, but its resemblance to undoubted Cordaitean species favours its attribution to that group though, as Mrs Arber points out, some markedly platyspermic seeds are known to have been borne on fern-like fronds and _Mitrospermum_ may belong to some genus of Pteridosperms.

=Diplotesta.= Brongniart.

_Diplotesta Grand’Euryana_ Brongniart. The generic name _Diplotesta_, suggested by Grand’Eury, was given by Brongniart[972] to a Grand’ Croix seed which he compared with that of the Conifer _Cephalotaxus_. The type-specimen is elliptical and platyspermic (fig. 495, H, p. 322), and differs from _Taxospermum_ in the cordate form of the seed-cavity, also in the more restricted union of nucellus and testa. The testa is differentiated into a sarcotesta (_sa_) and sclerotesta, and the latter forms two feebly developed keels in the principal plane: a characteristic feature shared with _Mitrospermum_ is the splitting of the shell into two equal valves (fig. 495, F). Fig. 495, H, shows the contracted cylindrical nucellus and the pollen-chamber: the sarcotesta (_sa_) is only partially preserved. _Diplotesta_ differs from _Cardiocarpus_ in the course of the integumental vascular bundles which are of the type illustrated by _Rhabdospermum_, _Taxospermum_, and _Cyclocarpus_, but from these genera it is distinguished by the dehiscence of the shell, also by its form and certain anatomical features as described by Brongniart and Bertrand[973].

In this genus Bertrand includes Brongniart’s species _Sarcotaxus avellana_ (fig. 495, F), a correlation suggested by the latter author.

=Leptocaryon.= Brongniart.

Brongniart[974] founded this genus for a single species, _Leptocaryon avellana_, represented by a Grand’ Croix specimen 12 × 10 mm., which he believed to be related to _Taxus_. _Leptocaryon_ differs from _Taxospermum_ in the structure of the testa, but resembles it in external features. Bertrand[975] in his revision and extension of Brongniart’s account says that the sections throw no light on the nature of the vascular supply, and it is therefore impossible to form a satisfactory opinion as to the relationships of the genus. Renault[976] referred this genus to the Cordaitales, but we have no evidence as to the parent-plant.

=Taxospermum.= Brongniart.

Brongniart[977] gave this name to a small elliptical seed, 15×9 mm., recalling in external features the seed of _Taxus_, a genus to which he believed the Grand’ Croix species to be related. The type-species _Taxospermum Grüneri_ (fig. 495, G) has a comparatively thin testa characterised by the absence of a sub-chalazal pad formed by the swelling of the sclerotesta. The nucellus is attached by a broad base to the testa and the two regions appear to be connected for a short distance on the flanks[978]; in this feature the seed is comparable with that of the Conifer _Torreya_ and differs from the other platysperms, _Diplotesta_, _Rhabdospermum_, etc. Bertrand[979] states that the main vascular strand extends from the hilum to the chalaza before giving off the two opposite bundles which ‘follow the floor of the shell-cavity, and on reaching the flanks traverse the shell obliquely from below upwards[980].’ In the course and position of the integumental bundles _Taxospermum_ differs from _Cardiocarpus_, _Cycadinocarpus_, and _Rhabdospermum_. In this genus Bertrand includes _Sarcotaxus angulosus_ Brongn. and _S. olivaeformis_ Brongn.[981]

=Compsotesta.= Bertrand ex Brongniart +MS.+

_Compsotesta Brongniarti_ Bertrand. The generic name _Compsotesta_[982], though adopted by Brongniart for some incomplete specimens from Grand’ Croix, was not published either by him or Renault: it has recently been revived by Bertrand[983] in his account of the anatomical details of Brongniart’s sections. This seed appears to be closely allied to the polypterous forms _Ptychotesta_ and _Hexapterospermum_: the testa consists of a sarcotesta differentiated into two zones the outer of which contains vascular bundles in correspondence with the ribs, and an inner shell. There is a nucellar vascular supply and the nucellus is free on the flanks as in _Stephanospermum_ and _Trigonocarpus_.

=Samaropsis.= Goeppert.

The characters of this Permian and Carboniferous genus have already been described: the name has reference only to superficial features especially the samara-like ‘wing,’ and connotes no special anatomical features.

_Samaropsis fluitans_ (Dawson). The species described by Dawson[984] as _Cardiocarpum fluitans_ from Carboniferous strata in Nova Scotia, is represented by oval seeds with a fairly broad border usually showing an apical notch. Fig. 502, A, is a copy of Dawson’s figure: the apparent absence of an apical sinus in the ‘wing’ is probably due either to an error in interpretation or to some imperfection in the specimen. As fig. 502, A, shows, the type-specimens are far from satisfactory, and it may be that they are not specifically identical with the more complete specimens from European strata referred to Dawson’s species. Zeiller[985] points out that seeds of this species vary considerably in size, but there is always in well-preserved examples a bifid beak at the apex. Seeds of similar form though not specifically identical are described from the Coal Measures of Missouri as _Cardiocarpon (Samaropsis) Branneri_ Fairch. and White[986]. Good examples of _S. fluitans_ are figured by Weiss[987] from the Coal Measures of Saarbrücken and the species is widely distributed in Upper Carboniferous beds generally.

_Samaropsis bicaudata_ Kidston. This species (fig. 502, E) originally described[988] from Lower Carboniferous rocks in Scotland as _Cardiocarpus bicaudata_ and subsequently assigned to _Samaropsis_, is characterised by a greater development of the flat wing-like border which is divided into two long tapering basal lobes. Seeds of similar form are figured by Lesquereux[989] from Pennsylvania as _Cardiocarpus_ (_Ptilocarpus_) _bicornutus_.

_Samaropsis_ (_Samarospermum_) _moravica_ (Helmhacher). This type[990] (fig. 502, H) is characterised by the great length of the wing-like border and on that account it was transferred by Arber to a new genus. It was originally described by Helmhacher from the Permian of Moravia as _Jordania moravica_ and the type-specimen has been refigured by Zeiller[991] who records the species from Upper Carboniferous and Permian rocks in France: it is recorded also from several localities in Germany[992]. Seeds figured by Potonié[993] from the Permian of Thuringia as _Samaropsis Crampii_ (Hartt) are undoubtedly examples of _S. moravica_: the true _S. Crampii_ has recently been well illustrated by Dr Stopes[994] from the Westphalian of New Brunswick. The species is recorded by Arber[995] from the Kent coalfield.

_Samaropsis emarginata_ (Goeppert and Barger).

The seed represented in fig. 502, B, from the Lower Coal Measures of Kilmarnock, Scotland[996], affords a good example of the genus: the species was originally described by Berger as _Cardiocarpon emarginatum_ and it was on this type that Fiedler founded the genus _Cyclocarpon_[997]. It has been referred by many authors to _Cardiocarpon_ and might be regarded as a type intermediate between _Cordaicarpus_, as used in this chapter, and _Samaropsis_, though the breadth of the border is more in keeping with the latter designation. The figured specimen is 1·6 cm. long and 1·4 cm. broad; the nucule has a slightly cordate base and shows several faint converging ribs which are too inconspicuous to be represented in a natural-size drawing. A narrow median groove in the apical region shows the position of a vascular strand. The species is recorded from several countries: similar though specifically distinct seeds, described by Dawson as _Cardiocarpon cornutum_, have recently been re-described by Dr Stopes[998] from the Westphalian of New Brunswick where they occur in association with the leaves of _Cordaites Robbii_ Daws.

_Samaropsis Newberryi_ Andrews.

This species was originally described by Andrews[999] from the Coal Measures of Ohio: the specimen shown in fig. 502, K, was sent to Dr Kidston by Mr Claypole. The whole seed is 5 cm. wide and 3·5 cm. in depth; it is characterised by a short and relatively broad nucule surrounded by a very broad and flat border showing faintly marked radially disposed lines and in places some irregularly distributed pits. The apex is emarginate and there is a broad and deep sinus in the sarcotesta in the chalazal region. The seed resembles _Samaropsis alata_ Kidst.[1000] and _S. Baileyi_ (Daws.)[1001] but it differs from these in the greater breadth of the ‘wing’ and in the form of the nucule.

The seed described by Fiedler[1002] as _Jordania bignonioides_ (fig. 502, I) agrees closely with _S. alata_ Kidst. but is probably specifically distinct.

_Samaropsis barcellosa_ (White).

White[1003] described this species (fig. 502, G) from Permo-Carboniferous rocks in Brazil (Rio Grande do Sul) as _Cardiocarpon barcellosum_. The nucule is said to be cordate but, as seen in the figure, there is no clear indication of a basal sinus: the presence of a relatively broad ‘wing,’ as White says, entitles the seed ‘to a place in the _Samaropsis_ section of the genus.’ The author of the species compares it with seeds described from Westphalian rocks in Ohio[1004] and Pennsylvania[1005]. It is interesting to find a type which is common in both Europe and North America in the western portion of Gondwana Land. Seeds of similar form are recorded also from India, South Africa, and Australia[1006].

_Samaropsis Seixasi_ (White).

This Brazilian species from the same beds is described by White as _Gangamopteris_ (_Samaropsis_) _Seixasi_[1007]: it is characterised by a small ovate nucule 8–10 mm. long and 5 mm. broad, in some specimens surrounded by a complete ‘wing’ extending above the apex and below the base, giving the seed an appearance similar to that of _Samaropsis_ (_Samarospermum_) _moravica_ while sometimes, as in the example shown in fig. 502, F, the broad border is preserved only at the sides. These seeds are abundant in the Santa Catharina beds, where they were discovered by Dr Esdras do Prado Seixas, in association with leaves of _Gangamopteris_, and White thinks that they were borne on the fertile leaves of that genus which he has named _Arberia_[1008]. Although there is as yet no proof of a connexion between _Gangamopteris_ and seeds of this or any other type it is almost certain that it was a seed-producing plant.

_Samaropsis Leslii_ sp. nov.

The seed on which this species is founded was discovered by Mr T. N. Leslie in the Ecca beds (Permo-Carboniferous) of Vereeniging, South Africa, a locality from which the same geologist has obtained leaves of _Cordaites_, _Psygmophyllum_, _Glossopteris_ and other genera[1009]. In the slightly cordate base and tapered apex (fig. 503) the nucule agrees closely with those of European examples, but the Vereeniging type is distinguished by its larger dimensions and by the wider border indicating a thick sarcotesta continued basally into a stout stalk. The apex is emarginate and a median rib marks the position of a vascular strand. There is no evidence as to the nature of the parent-plant.

_Samaropsis indica_ (Zeiller).

Prof. Zeiller[1010] described this species as _Cardiocarpus indicus_ from the Karharbari (Lower Gondwana) beds of India. An examination of the type-specimens enables me to confirm the accuracy of the original account. The platyspermic seed is 5·5 cm. long and 4·5 cm. broad; a cordate nucule is enclosed by a flat border similar to that of _Samaropsis Leslii_ but narrower especially on the sides of the nucule. At the apex there is a deep sinus extending to the nucule, and at the base a fairly broad band of carbonaceous matter shows the position of the chalazal vascular strand. The seed is characterised by its large size and by its almost orbicular form: it occurs as a detached specimen in beds containing _Cordaites_ (_Noeggerathiopsis_) and _Glossopteris_.

A species from Arkansas described by Lesquereux[1011] as _Cardiocarpus ingens_ [= _Cordaicarpus ingens_ (Lesq.)] affords another example of a large seed similar to _C. indicus_ and, except in its more orbicular form, to _Samaropsis Leslii_.

_Samaropsis Milleri_ (Feistmantel).

An examination of the type-specimen from the Calcutta Museum enables me to amplify the original description in an important particular. The species was found in Lower Gondwana (Katharbari) beds in India and referred by Feistmantel[1012] to the genus _Carpolithes_. Arber[1013], who tentatively employed the generic name _Cardiocarpus_ in place of _Carpolithes_, suggests that the seeds may be radiospermic, as Feistmantel’s drawings show only a very narrow border to the nucule. The specimen reproduced in fig. 504 was figured by Feistmantel without any indication of a definite sarcotesta or wing, but as seen in the drawing the ovate cordate sclerotesta is surrounded on one side and at the base by an outer envelope: this is clearly seen at the apex where it shows a rounded termination sloping downwards towards the micropyle precisely as in _Samaropsis indica_ (Zeill.). The border is narrow at the sides and broader at the base as in _S. Leslii_. The seed is 4·5 cm. long and 2·3 cm. broad, differing from _S. indica_ in its rather smaller size and in the slightly narrower nucule. Though there is no decisive evidence as to the parent-plant the occurrence of a specimen of this species partially covered by a scale-leaf of a type[1014] very similar to that which is generally recognised as belonging to _Glossopteris_ suggests the possibility that the seeds may belong to that genus. Scale-leaves of _Glossopteris_ are described in Volume +ii.+, but it may be added here that leaves similar in form to those from India, Australia, and elsewhere are figured by Geinitz[1015] from the Altai Mountains as _Trigonocarpus_? _actaeonelloides_: the specimens are represented with the basal scar at the apex.

=Cordaicarpus.= Geinitz.

In view of the fact that the generic names _Cardiocarpus_, _Cordaicarpus_, and other designations have been applied to casts and impressions which cannot be distinguished by any constant or important feature it is proposed to adopt the name _Cordaicarpus_ for platyspermic seeds, preserved as casts or impressions, having a comparatively narrow border enclosing an ovate or cordate-ovate nucule; the base is either rounded or cordate. The choice between _Cordaicarpus_ and _Samaropsis_ depends on the breadth of the border. _Cordaicarpus_, though more suggestive of a Cordaitean alliance, may in some cases be a Pteridosperm seed.

_Cordaicarpus Cordai_ (Geinitz). Lenticular seeds more or less orbicular or broadly ovate (fig. 502, C, D), often slightly cordate at the base of the nucule and with a broadly acute apex: the border is narrow or sometimes hardly represented as in the seeds described by Berger as _Rhabdocarpus ovoides_, a species similar to but more oval than _Cordaicarpus Cordai_. The latter species[1016] occurs in several coalfields in Britain, France, Germany, and elsewhere. Fig. 502, C, shows a good example from the Middle Coal Measures of Yorkshire, 9 mm. long by 8 mm. broad; on the very slightly cordate nucule are several faint ribs converging towards the base and apex and between them fine striations, characters too indistinct to be reproduced in the natural-size drawing. The flat border represents the sclerotesta. The seed shown in fig. 502, D, from the Westphalian series of Warwickshire belongs to the same species or is a closely allied type: the faint suggestion of reticulation on its surface might be regarded as a reason for referring it to _C. areolatus_ Boul.[1017], a form characterised by a reticulation on the testa, described by Zeiller[1018] and other authors. This reticulation is, however, in some cases at least, formed by crumpling and splitting of the superficial carbonised film into more or less regular meshes: the figured specimen occurs with several other seeds of the same type, most of which have a smooth surface. Dr Kidston tells me that a recent critical examination of seeds in his collection leads him to regard some specimens (_e.g._ fig. 502, D) previously referred by him to _C. Cordai_ as identical with _Carpolithes membranaceus_ Goepp.[1019]

The photograph reproduced in fig. 505 shows the result of chemically treating the carbonised cuticle of a seed of _Cordaicarpus Cordai_, a method little used as yet in the case of Palaeozoic plants but which may be useful in distinguishing seeds which cannot be satisfactorily separated by microscopic features. The superficial cells have very thick walls and present an appearance similar to that of the sclerous cells in the testas of some petrified specimens.

The larger seed shown in fig. 501, D, from Commentry, described by Renault and Zeiller[1020] as _Cardiocarpus sclerotesta_, is another example of _Cordaicarpus_ as now defined.

IV. +Miscellaneous Seeds.+

In this section are included genera based on characters of comparatively little morphological importance; their claim to treatment under a common heading is that we know little or nothing of their anatomical features or of the parent-plants.

i. _Ribbed seeds._

The seeds represented by the following genera possess ribs or flanges usually in multiples of three; the transverse section may be triangular, hexagonal, or polygonal. The symmetry is generally radial, but it is difficult to determine whether a slight departure from the radiospermic form is an original feature or the result of pressure. Some of the ribbed seeds with which we are now concerned are no doubt closely allied to _Trigonocarpus_ and should be included in the Trigonocarpales, but others may well be distinct forms.

Genera: _Hexagonocarpus_, _Decagonocarpus_, _Polypterocarpus_, _Rhynchogonium_, _Boroviczia_, _Diplopterotesta_, _Musocarpus_, _Holcospermum_.

=Hexagonocarpus.= Renault.

This generic name is adopted by Renault[1021] for casts from Commentry which, while probably identical with Brongniart’s _Hexapterospermum_, afford no confirmatory anatomical evidence. The species _Hexagonocarpus crassus_[1022] is represented by casts or nucules characterised by six well-defined ribs and grooves with a length of nearly 3 cm. In this genus may be included the cast from the Coal Measures of Lancashire described by Williamson[1023] as _Hexapterospermum Noeggerathi_ (fig. 506, H), and another British example is afforded by _Hexagonocarpus Hookeri_ Kidst.[1024], a rare fossil in the South Staffordshire coalfield. It is impossible confidently to assign these ribbed casts to genera founded on petrified specimens as they almost certainly belong to different types, but the employment of the name _Hexagonocarpus_ may conveniently be used for casts or impressions of seeds with six longitudinal ribs differing in their relatively broader and less prominent form from the wing-like flanges of _Polypterocarpus_ (cf. fig. 496, B). The seeds described by Dr P. Bertrand[1025] as _Hexapterospermum modestae_, and believed by him to belong to a plant with _Neuropteris_ fronds, should be included in _Hexagonocarpus_ as we have no definite knowledge of their anatomical features.

=Decagonocarpus.= Renault.

This name, proposed by Renault[1026], is applied to seeds without petrified tissues characterised by ten ribs; an example is afforded by _Decagonocarpus olivaeformis_ from the Commentry coalfield, an elliptical seed which bears a close resemblance to _Holcospermum sulcatum_ (fig. 506, A) except in the smaller number of ribs.

=Polypterocarpus.= Grand’Eury.

Grand’Eury[1027] adopted this generic name for seeds from St Étienne characterised by the presence of three, six, or more deep wings or flanges. The term _Pterospermum_ has recently been proposed by Arber[1028] for a seed from the Coal Measures of Staffordshire, which he names _P. anglicum_: the type-species of the genus has three deep wings, one from each angle. For the same seed Kidston[1029] proposed the name _Tripterospermum ellipticum_, but as Arber’s account was published first his specific name has priority. _Pterospermum_ had, however, been previously used for a genus of Sterculiaceae, and partly on this account but mainly because Grand’Eury’s genus _Polypterocarpus_ is available the latter designation is adopted. In _Polypterocarpus anglicus_ (fig. 496, B) the flanges project slightly beyond the apex of the seed and there is a small notch at the base; the nucule is 5 cm. long and 1 cm. broad. While it is not improbable that this seed is generically identical with Brongniart’s _Tripterospermum_[1030], it is safer, in the absence of structural details, to employ the less committal term. There is no information with regard to the nature of the parent-plants of species of _Polypterocarpus_. The English seed from the Middle Coal Measures of Derbyshire and the Staffordshire coalfield described by Arber[1031] as _Radiospermum ornatum_ and by Kidston[1032] as _Polypterospermum ornatum_ affords another example of _Polypterocarpus_ as the generic name is here employed.

=Rhynchogonium.= Heer.

Heer[1033] proposed this generic name for some globose, ovate, or oblong ‘fruits’ from Lower Carboniferous strata in Spitzbergen, including also fragments of ‘leaves’ which without satisfactory evidence he believed to belong to the same plant. The supposed fruits are clearly seeds, and Nathorst regards the ‘leaves’ as portions of a Fern rachis. Heer described four species, but these have since been reduced to two, and indeed it is probable that only one type, _Rhynchogonium costatum_, is represented. Nathorst[1034] compares Heer’s seeds with a Lower Carboniferous species described by Young[1035] as _Trigonocarpum gloagianum_, the resemblance of which to the Spitzbergen seeds was pointed out by Kidston. A seed of _Rhynchogonium costatum_ is about the size of a hazel-nut and may reach a length of 21 mm.; it is ovate, with a broad rounded base, and in the upper third is tapered and conical, the sides of the characteristic snout being distinguished from the smooth surface of the rest of the seed by the presence of eight ribs converging towards the apex (506, G). Zalessky[1036] recorded closely allied seeds from Lower Carboniferous beds in Northern Russia, assigning them to a new genus _Boroviczia_, the type-species being _B. Karpinskii_; he adduced arguments in favour of Heer’s interpretation of the fossils as fruits but, according to Nathorst, this view has been abandoned. In his recent memoir on the Culm flora of Spitzbergen Nathorst[1037] discusses the morphological nature of _Rhynchogonium_ seeds and describes additional specimens. Without the aid of petrified examples it is hardly possible to determine the true nature of the fossils.

Some specimens of _Rhynchogonium sulcatum_ in Dr Kidston’s collection show the original surface-features: the carbonised integument is divided in the upper region into linear lobes separated from one another at their origin by fairly wide sinuses, a type of integument suggesting comparison with _Physostoma_. This species was originally described by Lindley and Hutton as _Carpolithes sulcata[1038]_ from Lower Carboniferous rocks at Newhaven in Scotland and has recently been figured by Zalessky[1039] from specimens in the Kidston collection from the Lower Calciferous sandstone of Midlothian. Nothing definite can be said as to the parent-plant, but it is significant that in Midlothian _Rhynchogonium sulcatum_ occurs in a bed full of isolated pinnules of a _Cardiopteris_ almost to the exclusion of any other fossils[1040].

The seed figured by Nathorst[1041] from the Culm of Spitzbergen as _Lagenospermum? glandiforme_ agrees closely with _Rhynchogonium_ and _Boroviczia_, and it is impossible to decide whether the lobed appearance is due to the presence of a cupule or to the divisions of an integument.

=Boroviczia.= Zalessky.

The specimens from Lower Carboniferous beds in Russia[1042] on which this genus was founded are perhaps unnecessarily separated from _Rhynchogonium_; they are ovate and beaked, 10 mm. long with a maximum breadth of 6 mm. The type-species, _Boroviczia Karpinskii_ (fig. 506, I), is represented both by specimens in which the cast is complete and by others in which the apical snout of the integument is split into separate lobes identical in form and apparently in number with those of _Rhynchogonium_. Nathorst[1043], who retains the generic name and describes two additional species from Spitzbergen, points out that in Boroviczia the tapered apex is more sharply differentiated from the broader basal portion, a difference hardly worthy of generic recognition. If _Boroviczia_ is retained as a genus distinct from _Rhynchogonium_ it should include the seeds described by Young as _Trigonocarpum gloagianum_.

=Diplopterotesta.= Nathorst.

_Diplopterotesta spitzbergensis_ (Heer). Heer[1044] included in _Samaropsis_ some seeds, described as _Samaropsis spitzbergensis_, from Lower Carboniferous strata in Spitzbergen which differ considerably from typical examples of the genus. These have recently been made the type of a new genus _Diplopterotesta_[1045]: they are platyspermic seeds nearly twice as long as broad, 6–9 × 3·5–5 mm., characterised by a thin sclerotesta expanded throughout the length of the seed into two prominent transversely striated wing-like ribs or flanges (fig. 506, D). At the apex, which is broad in contrast to the pointed basal end of the seed, the sclerotesta forms a crown of eight lobes about the flat summit of the seed-body. As Nathorst points out, this species closely resembles the Carboniferous seeds figured by Grand’Eury[1046] as _Polypterocarpus_, but in the latter type there are more than two wings. Nathorst’s figures, one of which is reproduced in fig. 506, D, suggest a difficulty in determining the number of the flanges, which would seem to be more than two, but this appearance is regarded by Nathorst as misleading and he believes that except at the apex there are only two wings.

=Musocarpus.= Brongniart.

Brongniart[1047] proposed this name for two species, _M. prismaticus_ and _M. difformis_, from French Coal Measures, but gave no description of the specimens. The type-species, described from the Loire by Grand’Eury as _Musocarpus prismaticus_[1048], is an ovate seed nearly 3 cm. long with six longitudinal ribs, three being more prominent than the others, and characterised by a ribbed prolongation of the base of uniform diameter spoken of as a carpophore, which was apparently articulated to the lower part of the seed-proper from which it was easily detached by a natural absciss-layer. Nothing is known of the structure or of the affinity of the genus. Some specimens in Dr Kidston’s collection from Westphalian beds in Lanarkshire are closely allied to or perhaps identical with _M. prismaticus_. In the presence of a distinct basal region _Musocarpus_ resembles _Codonospermum_[1049], though without any knowledge of the anatomy of the former type it is impossible to say whether or not this resemblance has any morphological importance.

=Holcospermum.= Nathorst.

_Holcospermum sulcatum_ (Sternberg). The cast reproduced in fig. 506, A, affords a good example of a form of seed recorded under several generic names and not uncommon in Upper Palaeozoic rocks in Europe and North America, which in most cases cannot be assigned to a genus implying the possession of certain anatomical characters. This type was figured by Sternberg[1050] from the Coal Measures of Radnitz as _Carpolites sulcatus_. Some ‘fruits’ collected on the beach near Newhaven, Midlothian, from the Calciferous Sandstone series, are figured by Lindley and Hutton[1051] as _Carpolithes sulcata_, but as already stated these have been transferred[1052] to the genus _Rhynchogonium_. Several authors have referred specimens of the type now included in _Holcospermum_ to _Rhabdocarpus_, but that genus, as stated on a previous page, is restricted to seeds agreeing in form with _R. tunicatus_. Renault[1053] instituted the genus _Colpospermum_ for a partially petrified seed from Commentry agreeing externally with _Carpolites sulcatus_ Sternb. and regarded by him as specifically identical, characterised by longitudinal ribs which represent folds of the testa, the intervening grooves being occupied by an irregular reticulum formed by occasionally anastomosing smaller ribs. The generic name _Colpospermum_ should therefore be reserved for ribbed seeds showing the anatomical features described by Renault and Zeiller: its application to Sternberg’s species is inadvisable on the ground that we have no information with regard to the morphological nature of the ribbing. More recently Arber[1054] has proposed the name _Platyspermum_, a name previously applied to a Cruciferous plant, for Stephanian and Permian seeds formerly assigned to Berger’s genus _Rhabdocarpus_, which are symmetrical in two planes. In this genus he includes _Platyspermum sulcatum_ and among other species _P. Kidstoni_ founded on a seed originally identified by Kidston[1055] as _Rhabdocarpus multistriatus_ Sternb. which, though probably a distinct species, is of the same general type as _C. sulcatus_ Sternb.