Chapter XVI: Land and Fresh-Water Shells

DURING my numerous excursions in these islands, I had in the majority of instances to follow up the stream-courses in order to examine their geological structure. I had therefore good opportunities in these regions of making a collection of the fresh-water shells, which, together with the land shells I collected, formed a total of between sixty and seventy species, amongst which there were 11 new species and at least 5 new varieties, whilst about 14 would appear to have been never previously recorded from the Solomon Islands, and there were in addition several from new localities in the group. The collection was sent to the British Museum and was examined and described by Mr. E. Smith, to whose paper on the subject[479] I am indebted for my acquaintance with the shells in question, and through whose kindness I have been thus enabled to supplement my other observations in these islands. A list of the shells with the descriptions of the new species is given on page 344. For its size, my collection presented a large amount of novelty, coming as it did from a region the land and fresh-water shells of which were previously considered to be fairly known. There can be no doubt, however, that in the Solomon Islands the conchologist has much work that remains to be done. Not only are the higher regions of the larger islands, entirely unexplored, but it would appear from the collections made up to the present date in this large group, that particular species may be not only confined to a special sub-group of islands but may be restricted to a single island, and that other species more widely distributed through the group may be represented in each island and in different districts of the larger islands by different varieties. Had I been aware of the extent of the influence of locality in this region, I might have made my collection of greater value. It would therefore seem necessary for future collectors in this group to make in every small island and in different districts of the larger islands special independent collections, disregarding the fact that they may have apparently met with the same shell very frequently before, because many of the varieties and some of the species can only be distinguished by the practised eye of the specialist, and a new locality for a previously well-known species may be often unwittingly found.

[479] “On a collection of shells from the Solomon Islands” by Edgar
A. Smith. (Proceedings of the Zoological Society: June 2nd, 1885.)
This paper is illustrated with two coloured plates of the new
shells.

As an instance of the unexpected results, which may fall to the lot of others in this group, I may here add, that out of eleven land and fresh-water shells that I collected in the small island of Santa Anna, which is only 2½ miles in length, four were new species, and besides there were some new varieties. The stations of these four species may be suggestive. Two of them--_Helix_ (_Videna_) _sanctæ annæ_ and _Helix_ (_nanina_) _solidiuscula_--were generally found on the trunks of the cocoa-nut palms at the coast; whilst the other two occurred in situations far more likely to yield new species, _Melania sanctæ annæ_ being obtained from a small stream in the interior of the island, and _Melania guppyi_ being found dead in the stomach and intestines of a fish that frequents the fresh-water lake of Wailava. This last shell would appear to live in the deeper parts of the lake, as I only found one living specimen, all the others being obtained from the stomach and intestines of these fish. Mr. Smith describes it as “a very remarkable and distinct species.” Its length is about 1⅕ inches; and its sharp-pointed spire was to be sometimes seen protruding through the vent of the fish, which evidently digests the animal and ejects the shell. These fish were usually 9 or 10 inches long; but the full-grown shells were found also in fish half this size, when the relation between the length of the shell and the size of the fish was truly alarming. Since the little fish actually swallow sharp pointed shells measuring a fifth of their own length and pass them out through the vent after they have digested the animal, we must credit them with a remarkable capacity for adapting their diet to circumstances.

To exemplify the variation which some species of shells display in this group, I will take the instance of _Helix_ (_Geotrochus_) _cleryi_, Récluz. This species is probably distributed through the whole group; but considerable variation prevails in different islands. Amongst the several forms which I obtained, three were named as new varieties, var. _meridionalis_ from Santa Anna, var. _simboana_ from Simbo or Eddystone Island, and var. _septentrionalis_ from the islands of Bougainville Straits, the localities of the two last varieties being only 80 miles apart. Mr. Smith remarks that this species is “subject to considerable variation in size, colour, and form, apparently resulting from difference of habitat. . . . . . . . . Whether these several varieties should take specific rank is questionable, for, although there is a considerable difference between the extreme forms, even in the series of nearly one hundred specimens under examination, the gradual transition from one form to another is observable.”

Amongst the more singular in appearance of the land shells, I may refer to the large _Bulimus_ (_B. cleryi_) which I found on the north coast of St. Christoval. It attains a length of four inches. I was never able to get a living specimen, as they are said by the natives to live in the foliage of the high trees. The specimens which I obtained were empty shells which the natives of the Koofeh district on the north coast of St. Christoval are in the habit of throwing into heaps, each man when he picks up a shell throwing it into the next heap he passes. I was unable to learn the reason of this practice and the natives did not seem willing to tell me. . . . Two other _Bulimi_ I commonly met with. One was the pretty _Bulimus miltocheilus_ (Reeve), which, when the animal is young and the shell delicate, has a greenish-yellow hue resembling the colour of the leaves it feeds upon: as it grows older the shell becomes thicker and stronger, and in proportion as there is less need for protective resemblance, the greenish-yellow hue fades away, leaving a dull white colour behind. This species is found in St. Christoval and the adjacent islands. The other _Bulimus_ (_B. founaki_, Homb. Jacq.) which I found in Faro Island, Bougainville Straits, and which had been only previously obtained at Isabel Island, attains a length of rather under three inches.

I come now to refer to the fresh-water shells of these regions. Stated in their order of frequency, the _Neritinæ_, _Melaniæ_, and _Navicellæ_ are the common fresh-water shells of these islands. The _Neritinæ_ were especially interesting to me. They abound in the streams: some of them preferring the moist rocks above the water, others finding their home in the waters of a quiet pool, whilst others, like the _Navicellæ_, prefer to buffet the full rush of the torrent. An important feature with reference to these fresh-water Nerites or _Neritinæ_ is their wide dispersal. “Some of these species”--as Mr. Smith remarks in respect of those in my collection--“range not only through most of the islands of the Solomon Group, but have a considerably wider distribution.” Thus, _Neritina subsulcata_ (Sowerby) and _N. cornea_ (Linné), are not only found in the Solomon Islands, but also occur in the Philippines: _N. macgillivrayi_ (Reeve) and _N. petiti_ (Récluz) alike exist in the Fiji and in the Solomon Groups; while _N. porcata_ (Gould) has been found in Samoa and in Fiji as well as in the opposite extremities of the group with which I am at present concerned. Being interested in the question of the mode of dispersal of these Nerites, I made the following experiment to test their powers of sustaining submersion in salt-water. One individual belonging to the species _Neritina subsulcata_[480]--a species which is also found as above stated in the Philippines, and at the same time is the most widely dispersed fresh-water Nerite in the Solomon Group--survived a submersion of twelve hours; but not one out of a dozen individuals was found alive after a submersion of five days, although the water was changed from time to time. The result was a surprise to me, as I inferred from the result of Baron Aucapitaine’s experiments as related by Mr. Darwin,[481] that their close-fitting stony _opercula_ would have enabled them to resist the action of salt-water. Their death could have been scarcely due to want of food, since I have kept shells of this species for several months on a very scanty diet, and since the powers of endurance of other fresh-water shells are well known. The matter passed out of my mind until after my arrival in England, when Mr. Smith put the question to me, as to their mode of dispersal. I then remembered that their calcareous egg-capsules, which are so commonly seen on the rocky sides of the streams, are in all probability sufficiently thick to resist the action of salt-water. Here is therefore a probable mode of dispersal, and I see it is one which Mr. Smith refers to as such in his paper. These egg-capsules “if attached to floating timber, might be carried to considerable distances.” They are often to be observed on the outside of the shells of living _Navicellæ_, and I have seen them on the backs of the valves of a _Unio_ which I discovered in the Shortland Islands.

[480] In his paper Mr. Smith refers to the species experimented on
as _N. cornea_: but in my own list he named a shell belonging to one
of the _Neritinæ_ in question as _N. subsulcata_.

[481] _Cyclostoma elegans_ was the species tested: _vide_ “Origin of
Species,” p. 353, 6th edit.

One common feature of these fresh-water shells, whether _Neritinæ_, _Navicellæ_, or _Melaniæ_, is the extensive erosion of the apices and surrounding parts of the shells. In some instances I have noticed that almost the entire exterior of the shell has been extensively eroded, particularly in the case of _Neritina subsulcata_, but I always found that the erosion was greatest in non-calcareous districts, where the free carbonic acid in the water is not all consumed in the solution of the limestone rocks. In volcanic islands the erosion of the fresh-water shells is greater than in islands of calcareous formation; and in streams, which, like those of the north coast of St. Christoval, flow in the upper portion of their course through a district of volcanic rocks and in the lower portion through a district of calcareous rocks, the same difference in the degree of erosion may be observed. I learn from a recent work by Professor Semper[482] that it is the boring of a minute fungus which first exposes the calcareous substance to the action of the carbonic acid, and that the mechanical action of the stream in forming tiny whirl-pools in the cavity probably assists in the erosion.

[482] “The Natural Conditions of Existence, etc:” London 1881: p.
212, circâ.

There are two common species of _Neritina_ in these islands which I often confounded, viz., _N. subsulcata_ and _N. cornea_; and I learn from Mr. Smith’s paper that these two species very closely approach each other. They, however, are usually to be found in different stations, _N. cornea_ occurring on the trunks of palms and other trees away from the streams,[483] and _N. subsulcata_ preferring the moist rocky sides of the streams a foot or so above the water.[484] Now and then they may be found encroaching on each other’s domain; for I have found them together on the trunks and branches of areca palms and tree-ferns in low lying moist districts, whilst, as at Choiseul Bay, I found them together in the streams.[485] Now it is a significant circumstance, that the specimen of _N. cornea_ in my collection which was found by Mr. Smith to make the nearest approach to _N. subsulcata_ was one which I obtained from a stream in Choiseul Bay. It had, in this case, not only intruded on the station of _N. subsulcata_, but had also assumed some of the distinctive characters of that species. It, therefore, seems to me probable that a graduated series of the shells of these two species might be formed, which would present the stages of transition from the one species to the other. If this be possible, then I would suggest that the fresh-water Nerite (_Neritina subsulcata_) may have been transformed into the tree Nerite (_Neritina cornea_) in the following manner.

[483] In St. Christoval I found this species on one occasion 150
feet above the nearest stream.

[484] This species often takes to the water. Some individuals that I
kept alive on board used to spend a quarter of an hour at a time in
the water eating voraciously all the while.

[485] According to Prof. Semper, these two species in the
Philippines live a large portion of the year high up on the trees in
mangrove swamps. (Ibid.)

I have already referred to the circumstance that in the higher portions of the St. Christoval streams, where the rocks are entirely volcanic, the fresh-water shells--and I may here add, especially those of _Neritina subsulcata_--suffer much more erosion than do shells of the same species in the lower parts of the streams where they flow through calcareous districts. Now, the geological structure of this island being mainly ancient volcanic rocks incrusted near the coast by recent calcareous formations, the time will come when these calcareous envelopes will have been entirely stripped off by denudation. How this will influence the Nerites of the streams may be thus explained. At present the normal characters of the species are preserved in the calcareous portions of the streams; but when all the calcareous rocks have been stripped off by denudation, the Nerite through its whole lifetime will be subjected to that extensive process of erosion, which now often denudes almost the entire surface of the shells of those individuals that live in the volcanic portion of the stream’s course. Here, Natural Selection may step in to favour the survival of any slight variation that makes the Nerite more suited to lead an entirely arboreal existence. Such a geological agency may in truth lead finally to the expulsion of the Nerite from the stream’s course. Varieties will survive only in proportion to their capability of adapting themselves to the new condition; and they alone will perpetuate their kind until a tree Nerite of distinct specific character is produced. . . . . On this reasoning, tree Nerites ought to be more numerous in islands of volcanic formation; but this is a point on which I cannot pronounce from the lack of sufficient evidence.[486]

[486] Prof. Semper’s observations in the Philippines bear on this
matter. (“Natural Conditions of Existence,” &c., p. 188.)

According to Professor Semper, we have in _Navicella_ “a modified form of _Neritina_,” which genus it resembles in all essential anatomical characters, but “by long inurement to living in rushing mountain streams, it has had its shell modified in the way most suited to those conditions, while the _operculum_, in consequence of long disuse, has become a peculiar degenerate or rudimentary organ.”[487]

[487] Ibid, p. 212.

The growth of the fresh-water Nerites would appear to be slow. I kept a young individual of _Neritina subsulcata_ for seven months in a bottle partly filled with rain-water, and supplied it with decaying leaves for food which it used to eat. Its weight was 37 grains both at the beginning and the end of the experiment, having only varied half a grain during the whole time; and its dimensions, as determined by measurement, were unaltered. This species, when it is first picked off the rock, ejects a watery fluid with a powerful musky odour, which effect accompanies the closure of the shell by the _operculum_. I kept some individuals of this species in rain-water, containing varying proportions of lime-water, for about three months. The lime-water was of the medicinal strength of the British Pharmacopeia. I began with water containing 64 parts of rain-water to one part of the lime-solution. By the end of the first month the proportion was increased to 32 to 1; by the end of the second month it was 16 to 1; towards the end of the third month the Nerites, having lived for over three weeks in the last solution, began to die; the survivors were placed in a solution containing the proportion of 8 to 1, but this amount of the lime-solution proved too much for them. It should be remarked that throughout the experiment, the Nerites used to descend to the water to get their food just as frequently as in the state of nature: they did not avoid the water; and after the experiment was over, there was no apparent alteration in the appearance of the shells. These observations were made in the north part of New Zealand during the latter part of the summer and the beginning of the autumn, a circumstance which may partially explain the death of the shells. The temperature there was about 20° below the temperature they are accustomed to in the Solomon Islands; this difference is of interest when it is remembered that _Neritinæ_ are mostly found in the streams of tropical regions; and I may, therefore, infer that this species is capable of adapting itself to temperatures much lower than that to which it is accustomed, since some individuals survived the voyage to New Zealand from the Solomon Islands and lived in the climate of the former region for three months under very unfavourable conditions.

Professor Semper[488] remarks that some _Neritinæ_ have the habit of detaching themselves from rocks on the slightest touch, by this means, as he considers, escaping the pursuit of their enemies. Some of them, however, as I observed, detach themselves spontaneously and independently of any alarm. The individuals of _Neritina subsulcata_ that I kept in a large bottle in my cabin, used frequently in the course of a night to detach themselves from the sides and drop down into the water below. On one occasion when the noise woke me up, I found the culprit voraciously eating a portion of decayed leaf. In the daytime they sometimes dropped, and at other times crawled, down to the water. . . . . . It is probable that the musky water, which this Nerite ejects when it is picked off a rock, may cause a bird to drop it from its beak and thus save its life.

[488] Ibid, p. 210.

Amongst the new fresh-water shells that I found in this group was a species of _Unio_, to which Mr. Smith did me the honour of attaching my name, it being the first species of this genus of river-mussels that has been found in the Solomon Group. But its occurrence there means something more than a new locality, since, as I believe, I am correct in asserting, we have in it the first record of this widely distributed genus having reached the Pacific islands. I do not think that this species can be generally spread through the Solomon Group. I only found it in one locality, namely the Shortland Islands, near the western end of the group.

A very familiar shell, in low-lying moist and marshy situations throughout the Solomon Islands, is that of the auriculoid, _Pythia scarabæus_, Linné. Being usually accustomed to find it in the low-lying districts, I was surprised on one occasion to find it in the higher parts of Faro Island, which attains an elevation of 1,900 feet above sea. In the mangrove swamps and in the lower parts of the streams at Choiseul Bay, I found a species of _Cyrena_ which has not yet been described, together with _Cerithidea cornea_ (A. Adams: var.) and _Pyrazus palustris_, the last species occurring also in India. On the moist ground of the taro patches in the islands of Bougainville Straits thrives a species (_S. simplex_, var.) of that ubiquitous genus _Succinea_. The operculated land-snails, of which the _Helicinæ_ are the most numerous, are found more frequently in calcareous districts.

LIST OF LAND AND FRESH-WATER SHELLS COLLECTED IN THE SOLOMON ISLANDS[489] DURING 1882 AND 1883. (EXTRACTED FROM MR. E. SMITH’S PAPER IN THE PROCEEDINGS OF THE ZOOLOGICAL SOCIETY OF LONDON, JUNE, 2ND, 1885.) THE DESCRIPTIONS OF THE NEW SPECIES AND VARIETIES FOLLOW:

[489] The habitats given are confined to the Solomon Group. I have
added the new habitats of species in my collection to those
previously ascertained from the collections of Brenchley,
Macgillivray, Hombron and Jacquinot, etc.

(1) _Helicarion planospira_ (Pfeiffer) _Hab._ Santa Anna, Ugi, St.
Christoval, Guadalcanar.

(2) _Helix_ (_Nanina_) _nitidissima_ (nov. spec.) _Hab._ Treasury
Island, a variety in Guadalcanar.

(3) _Helix_ (_Nanina_) _solidiuscula_ (nov. spec.) _Hab._ Santa
Anna, found generally on the trunks of cocoa-nut palms.

(4) _Helix_ (_Corasia_) _tricolor_ (Pfeiffer) _Hab._ St. Christoval,
Ugi, Santa Anna.

(5) _Helix_ (_Corasia_) _anadyomene_, A (Adams & Angas) _Hab._
Guadalcanar, Ugi.

(6) _Helix_ (_Geotrochus_) _acmella_ (Pfeiffer) _Hab._ Faro Island,
Bougainville Straits; Florida Islands, _vide_ original paper.

(7) _Helix_ (_Geotrochus_) _gamelia_ (Angas) _Hab._ Isabel, Stephen
Island, Shortland Islands, Treasury Island, Choiseul Bay.

(8) _Helix_ (_Geotrochus_) _hargreavesi_ (Angas) _Hab._ Faro Island
in Bougainville Straits.

(9) _Helix_ (_Geotrochus_) _mendana_ (Angas) _Hab._ Shortland
Islands, _vide_ original paper.

(10) _Helix_ (_Geotrochus_) _motacilla_ (Pfeiffer) _Hab._ Simbo or
Eddystone Island, also called Narovo.

_Note._--In the original paper, Simbo and Eddystone are referred to
as two different islands. This mistake arose from the omission of
the name of Simbo in the latest charts; it is, however, the name
usually employed.

(11) _Helix_ (_Geotrochus_) _guppyi_ (nov. spec.) _Hab._ Faro Island
in Bougainville Straits.

(12) _Helix_ (_Geotrochus_) _dampieri_ (Angas) var. _Hab._ Choiseul
Bay.

(13) _Helix_ (_Geotrochus_) _eros_ (Angas) _Hab._ Isabel, Stephen
Island, Shortland Islands.

(14) _Helix_ (_Geotrochus_) _cleryi_ (Récluz) _Hab._ Santa Anna,
Ugi, St. Christoval, Guadalcanar, Rua Sura Islets, New Georgia,
Simbo or Eddystone, Treasury, Shortlands, Choiseul Bay. Three new
varieties, var _meridionalis_ (Santa Anna), var _simboana_ (Simbo or
Eddystone), var _septentrionalis_ (Shortlands, Treasury, Choiseul
Bay.)

(15) _Helix_ (_Videna_) _merziana_ (Pfeiffer) _Hab._ St. Christoval,
New Georgia, Ugi; _vide_ original paper.

(16) _Helix_ (_Videna_) _sanctæ annæ_ (nov. spec.) _Hab._ Santa
Anna, living on the trunks of cocoa-nut palms.

_Note._--This species, or a closely similar form, was observed by me
in many other islands; but I neglected to collect it in any other
locality than Santa Anna.

(17) _Helix_ (_Rhytida_) _villandrei_ (Gassies) _Hab._ St.
Christoval, Ugi.

(18) _Helix_ (_Camæna_) _hombroni_ (Pfeiffer) _Hab._ Shortland and
Faro Islands in Bougainville Straits, Isabel.

(19) _Helix_ (_Chloritis_) _eustoma_ (Pfeiffer) _Hab._ New Georgia,
Ugi, Faro Island (Bougainville Straits.)

(20) _Bulimus_ (_Placostylus_) _cleryi_ (Petit) _Hab._ St.
Christoval.

(21) _Bulimus_ (_Placostylus_) _founaki_ (Hombron and Jacquinot)
_Hab._ Isabel, Faro Island (Bougainville Straits).

(22) _Bulimus_ (_Placostylus_) _miltocheilus_ (Reeve) _Hab._ St.
Christoval (S.E. part), Ugi, Santa Anna: _vide_ original paper.

(23) _Partula_, spec. _Hab._ Guadalcanar, Ugi, Treasury Island,
Choiseul Bay: _vide_ original paper.

(24) _Succinea simplex_ (Pfeiffer) var. _Hab._ Treasury Island,
Shortland Islands: living on the moist ground in the taro patches.

(25) _Cyclostoma_ (_Adelostoma_) _triste_ (Tapparone Canefri), var?
_Hab._ Guadalcanar; Santa Anna; Faro and Shortland Islands and
Choiseul Bay in Bougainville Straits.

(26) _Leptopoma jacquinoti_ (Pfeiffer) _Hab._ Rua Sura Islets off
the north coast of Guadalcanar: _vide_ original paper.

(27) _Leptopoma vitreum_ (Lesson) _Hab._ Santa Anna, Simbo or
Eddystone; Shortland Islands.

(28) _Omphalotropis nebulosa_ (Pease) _Hab._ St. Christoval,
Guadalcanar, Ugi. I found this shell living on trees clothing a low
tract of land skirting the beach.

(29) _Pupina solomonensis_ (nov. spec.) _Hab._ Shortland and
Treasury Islands in Bougainville Straits: living in the decayed
trunks of fallen trees.

(30) _Hargravesia polita_, H. (Adams), var. _Hab._ Faro Island in
Bougainville Straits: _vide_ original paper.

(31) _Helicina moquiniana_ (Récluz) _Hab._ St. Christoval,
Guadalcanar, Ugi.

(32) _Helicina egregia_ (Pfeiffer) _Hab._ Guadalcanar, Florida
Islands.

(33) _Helicina modesta_ (Pfeiffer) _Hab._ Guadalcanar, Shortland
Islands, Treasury Islands, Choiseul Bay.

(34) _Helicina solomonensis_ (nov. spec.) _Hab._ The Islands of
Bougainville Straits (Faro, Shortlands, Treasury).

(35) _Pythia scarabæus_ (Linné) _Hab._ Santa Anna, St. Christoval,
which were the localities of my specimens; but I observed this
species and its varieties in every island I visited. _Stat_: Moist
ground usually near the sea.

(36) _Melampus fasciatus_ (Deshayes) _Hab._ Isabel, Rua Sura Islets
off the north coast of Guadalcanar. I found these shells in the
crevices of a log on the beach.

(37) _Melania amarula_ (Linné) _Hab._ Ugi, in the streams.

(38) _Melania scabra_ (Müller) _Hab._ Ugi, in a stream.

(39) _Melania salomonis_ (Brot.) _Hab._ Ugi, in a stream.

(40) _Melania fulgurans_ (Hinds) _Hab._ Ugi, in a stream.

(41) _Melania fastigiella_ (Reeve) _Hab._ Imbedded in a dark
calcareous loam exposed in the banks of a large stream near its
mouth at Sulagina, on the north coast of St. Christoval. I could not
find any living specimens.

(42) _Melania_ spec. _Hab._ The same as _Mel. fastigiella_.

(43) _Melania verrucosa_ (Hinds) _Hab._ The same as _Mel.
fastigiella_.

(44) _Melania subgradata_ (nov. spec.) _Hab._ The same as _Mel.
fastigiella_.

(45) _Melania ugiensis_ (nov. spec.) _Hab._ From a stream in Ugi.

(46) _Melania sanctæ annæ_ (nov. spec.) _Hab._ A stream in the
interior of Santa Anna.

(47) _Melania guppyi_ (nov. spec.) _Hab._ From the stomach and
intestines of a fish living in the fresh-water lake of Wailava in
the island of Santa Anna. This species probably frequents the deeper
parts of the lake, as I only found one living individual.

(48) _Cerithidea cornea_ A. (Adams) var. _Hab._ Mangrove swamps in
Choiseul Bay.

(49) _Pyrazus palustris_ _Hab._ Mangrove swamps in Choiseul Bay.

_Note._--Not referred to in original paper.

(50) _Nerita marmorata_ (Hombron and Jacquinot) _Hab._ Living just
above high-water level on the surface of the coral-limestone coast,
St. Christoval.

(51) _Neritina cornea_ (Linné) _Hab._ Star Harbour, St. Christoval,
on the trunks of trees 150 feet above the nearest stream; Choiseul
Bay, from a stream; Shortland Islands, on the stems of tree-ferns
and areca palms in a marshy district. I found this species in many
other islands; but did not collect it except in the above three
localities.

(52) _Neritina subsulcata_ (Sowerby) _Hab._ Streams in St.
Christoval and in the islands of Bougainville Straits. In the
Shortland Islands I found this species on the stems of tree-ferns
and areca palms in a marshy district. I only collected it in these
localities; but I found it in many other islands. When first picked
off the rock, it ejects a watery fluid possessing a powerful musky
odour.

(53) _Neritina dubia_ (Chemnitz) _Hab._ Shortland Islands, in a
stream.

(54) _Neritina adumbrata_ (Reeve) _Hab._ A stream in Choiseul Bay,
and the rocky sides of a stream-course in Ugi.

(55) _Neritina pulligera_ (Linné) _Hab._ Guadalcanar, St.
Christoval, Ugi, Choiseul Bay, in the streams.

(56) _Neritina petiti_ (Récluz) _Hab._ Treasury and Faro Islands, in
the streams.

(57) _Neritina olivacea_ (Le Guillou) _Hab._ Streams in Treasury
Island and at Sulagina, St. Christoval.

(58) _Neritina macgillivrayi_ (Reeve) _Hab._ Streams in Guadalcanar
and in Faro Island, Bougainville Straits.

(59) _Neritina asperulata_ (Récluz) _Hab._ Rocky sides of a
stream-course in Ugi.

(60) _Neritina porcata_ (Gould) _Hab._ St. Christoval, and Faro
Island, Bougainville Straits, in streams.

(61) _Neritina variegata_ (Lesson) _Hab._ St. Christoval, Ugi; Simbo
or Eddystone; Faro Island, Bougainville Straits; Choiseul Bay; in
streams.

(62) _Neritina turtoni_ (Récluz) _Hab._ A stream in the Shortland
Islands; streams in Guadalcanar; imbedded in a dark calcareous loam
exposed in the banks of a large stream near to its mouth at Sulagina
on the north coast of St. Christoval.

(63) _Neritina brevispina_ (Lamarck) _Hab._ Streams in Shortland,
Treasury, and Ugi Islands. The specimens from Treasury Island were
destitute of spines.

(64) _Neritina squarrosa_ (Récluz) _Hab._ Streams in Treasury
Island.

(65) _Navicella sanguisuga_ (Reeve) _Hab._ Streams in Faro Island,
Bougainville Straits.

(66) _Navicella suborbicularis_ (Sowerby) _Hab._ Guadalcanar, St.
Christoval, Ugi, Treasury and Faro Islands in Bougainville Straits.

(67) _Unio guppyi_ (nov. spec.) _Hab._ Streams in the Shortland
Islands.

(68) _Cyrena_, spec. _Hab._ In the lower parts of streams and in
mangrove swamps, Choiseul Bay. _Note._--This species is not referred
to in the original paper.

_Descriptions of the new species and varieties_,[490] by Mr. E. Smith.

[490] The numbers refer to the plates in Mr. Smith’s paper (Proc.
Zool. Soc., June 1885).

(2) _Helix_ (_Nanina_) _nitidissima._ (Plate XXXVI. figs. 1, 1 _b_.)
Shell thin, transparent, very glossy, depressed, narrowly perforate,
pale brownish horn-colour above, whitish towards the umbilicus,
sculptured with very faint lines of growth. Whorls 4-5, slightly
convex, impressed and marginate above at the suture; last whorl
large, rounded at the periphery. Aperture obliquely lunate;
peristome simple, thin, slightly thickened and reflexed partly over
the perforation. Spire low, but very little raised above the last
whorl, obtuse at the apex. Greatest diameter 14 millim., smallest
12; height 9.

(3) _Helix_ (_Nanina_) _solidiuscula._ (Plate XXXVI., figs. 2, 2
_b_.) Shell very narrowly perforate, depressed, somewhat solid, dark
chestnut-brown and a little glossy above, more shining and paler
beneath, becoming almost white at the umbilical region; whorls 6½,
convex, separated by a deepish suture, and, with the exception of
two or three at the apex which are smooth, sculptured with strong,
close-set, arcuate, and oblique striæ on the upper surface, crossed
with a few more or less distinct spiral lines. Body-whorl rounded at
the periphery, or sometimes with the faintest indication of an
angle, convex, and only exhibiting fine lines of growth below.
Aperture obliquely semi-lunate; peristome simple, but, owing to the
solidity of the shell, seeming slightly thickened, especially on the
very oblique columellar margin, which is shortly reflexed above over
the perforation. Spire depressed-conoid, having the least convex
outlines and an obtuse apex. Greatest diameter 18 millim., smallest
16½, height 12; aperture 8 long, 4½ wide.

This species is well distinguished by its comparative solidity and
strong sculpture on the upper surface.

(4) _Helix_ (_Corasia_) _tricolor_ (Pfeiffer). (Plate XXXVI., figs.
3, 3 _b_.) A specimen obtained on the north coast of the same island
of St. Christoval, by Mr. Guppy, is worthy of special mention, and
may be termed var. _picta_, on account of the undulating
reddish-brown stripes which ornament both the upper and lower
surfaces.

A similar example was also collected by Dr. A. Corrie and presented
to the Museum. The markings on these two shells are very striking
and distinctly visible within the aperture.

(11) _Helix_ (_Geotrochus_) _guppyi._ (Plate XXXVI. fig. 4.) Shell
elevately conical, thin, pale yellow, ornamented with conspicuous
nearly black or black-brown spiral bands, one above and one below
the sutures of the upper whorls, and three upon the last, one
sutural, the second peripheral, and the third basal. Volutions 6,
rather slowly enlarging, a little convex, sculptured with fine
oblique striæ of growth, not glossy. Three first whorls livid
purplish, the last rather sharply angled at the middle, not
descending in front, having the basal band broad around the almost
concealed perforation, and obsolete within the aperture. The latter
is oblique, somewhat narrowed and pouting in front, banded within
with three almost black and two white bands, the central one of the
former being squarely truncate at the end, only the lower corner of
it touching the margin of the lip, which is pale oblique, receding,
a little expanded and reflexed in front and at the columellar
margin, the upper end of which is spread over and nearly conceals
the small umbilicus. Height 22½ millim., greatest diameter 19,
smallest 16.

This species is remarkable for the striking contrast of its
colour-bands and the angular character of the last whorl.

(12) _Helix_ (_Geotrochus_) _dampieri_, Angas, var. (Plate XXXVI.
fig. 5.) Shell imperforate, subglobose, conoid, light brown or
fawn-colour, here and there minutely dotted with dark-grey specks,
with a broad white band around the middle of the penultimate whorl
and two upon the last, one above and the other below the middle,
also a narrow white line revolving up the spire beneath the suture,
and a dark brown zone surrounding the pale or yellowish umbilical
region. Whorls 5, a little convex above, somewhat glossy, obliquely
and very finely striated by the lines of growth, the last more or
less concentrically striated beneath, shortly descending at the
aperture which is white within. Lip a little thickened, edged with
reddish brown, only slightly expanded on the right side, more
dilated below, produced into a thin transparent callosity over the
umbilical region, united above to the upper extremity of the
peristome. Columellar margin oblique, white or partly tinged with
reddish brown, thickened and terminating below within the edge of
the lip. Height 19 millim., greatest diam. 22, smallest 19.

The specimens from the Solomon Islands are smaller than the type
with which, through the kindness of Mr G. F. Angas, I have compared
them. They also have the peristome brown, and the basal band is
darker.

(14) _Helix_ (_Geotrochus_) _cleryi_, Récluz (Plate XXXVI. figs 6, 6
_b_). The specimens from Santa Anna (var. _meridionalis_ fig. 6 _b_)
are smaller than the type, pale brown above, with a white
thread-like line at the suture, and the acutely keeled periphery,
paler beneath, especially towards the centre, and have the aperture
particularly acuminate at the termination of the keel.

The specimens from Simbo (var. _simboana_, fig. 6 _a_) are uniformly
pale horn-colour, rather sharply carinate at the middle, and have
the peristome white, considerably thickened and almost notched at
the upper end of the columella, and the body-whorl is more
contracted than in the typical form. The examples from Choiseul Bay,
Shortland and Treasury Islands (var. _septentrionalis_, fig. 6) are
all alike, of smaller dimensions than the normal form, thin pale
brownish horn-colour, with rather more convex whorls than usual, the
carina at the periphery being acute and thread-like as in the
variety _simboana_.

Whether these several varieties should take specific rank is
questionable, for, although there is considerable difference between
the extreme forms even in the series of nearly one hundred
specimens under examination, the gradual transition from one form
to another is observable.

(16) _Helix_ (_Videna_) _sanctæ annæ._ (Plate XXXVI. figs. 7. 7
_b_.) Shell depressed-conoid, deeply umbilicated, very acutely
keeled at the periphery, light brown, sometimes with a few radiating
pale streaks on the upper surface, sculptured with oblique lines of
growth. Whorls 5, rather slowly increasing, slightly convex,
depressed and margined above the suture, last not descending,
compressed above and below the keel, a little convex towards the
umbilicus, which is moderately large. Aperture transverse,
flesh-tinted within. Peristome simple, a little thickened along the
basal margin, with the extremities united by a thin callus. Height 7
millim.; greatest diameter 17, smallest 15.

(25) _Cyclostoma_ (_Adelostoma_) _triste_, Tapparone Canefri, var.?
Dr. Tapparone Canefri has kindly compared specimens from these
islands with his _C triste_, and is of opinion that they may be
considered a variety of it; and observes that the New-Guinean form
is a little smaller, its spire a little more slender, its surface
more glossy, the colour redder, and the apex of the spire darker.

The shells under examination are clothed with a very thin epidermis
when in a fresh condition, exhibiting numerous very fine spiral
thread-like lines, which entirely disappear in worn shells and can
easily be rubbed off with a brush. For several species having a
similar epidermis and an incomplete peristome, Dr. Tapparone Canefri
has proposed the subgenus _Adelostoma_.

(29) _Pupina solomonensis._(Plate XXXVI. fig. 9, 9 _a_.) Shell small
and very like _P. difficilis_, Semper, and _P. keraudreni_, Vignard.
It is of a reddish tint, especially the body-whorl; consists of 5½
whorls, which are the least convex and exhibit a pellucid line,
frequently brown, immediately beneath the suture. Last whorl very
obliquely descending behind, narrowed below, and flattened somewhat
above the aperture. Columella thickened with callus, white, parted
off from the whorl above by an oblique circumscribing red line,
truncated rather low down. Outer lip slightly thickened and effuse,
and a little paler than the rest of the whorl, produced somewhat at
its junction with the body-whorl, which in consequence has the
appearance of rising suddenly after an oblique descent. Length 7
millims., diam. 3⅔, aperture 2 long and wide.

(34) _Helicina solomonensis._ (Plate XXXVI. figs. 11, ll _b_.) Shell
small, globose-conical, reddish or yellowish, pale at the apex.
Whorls 4--4½, the least convex above, sculptured with lines of
growth and fine spiral striæ both on the upper and lower surfaces,
very faintly margined above at the suture; last whorl rounded at the
periphery, obsoletely angled near the junction of the outer lip and
the least descending in front, so that the faint angulation is
visible for a short distance above the sutural line. Aperture
somewhat semicircular and oblique, small; peristome slightly
expanded; umbilical callosity yellowish or pellucid whitish, defined
towards the base of the columellar margin. Greatest width 4⅔
millim., smallest 4; height 3½.

(44) _Melania subgradata._(Plate XXXVII. fig. 3, 3 _a_). Shell
elongate, turreted, rather solid, covered with an (olive?)
epidermis, and marked with fine longitudinal oblique red lines which
extend from suture to suture. Whorls probably about 10, flat or even
a little concave at the sides, shouldered above, usually with a
spiral shallow groove and a few striæ near the shoulder, and marked
with fine incremental striæ. Suture deep, slightly oblique. Last
whorl long, finely transversely striated, most distinctly at the
base. Aperture elongate-pyriform, acute above, effuse at the base.
Outer lip thin, sharp, accurate, and prominent at the middle.
Columellar margin rather thickly covered with callus, united above
to the outer lip. Length of two specimens, consisting of five whorls
30 and 25 millim.; diameter 11 and 10½; aperture 14 and 12 long, 6
and 5 wide.

(45) _Melania ugiensis._ (Plate XXXVII. fig. 4.) Shell subulate,
acuminate, beneath the epidermis (which is wanting in the specimens
at hand), of a dirty, pale, livid, or purplish tint. Whorls probably
about 14 in number; the eleven remaining are a little convex, rather
slowly enlarging, and sculptured with close-set, obliquish, fine
riblets, which are crossed by crowded spiral striæ. Last whorl
large, with the riblets rather obsolete below the middle, and very
close together, much more numerous than those upon the upper whorls.
Aperture obliquely pear-shaped. Length 25 millim., diameter 8;
aperture 8½ long, 4½ wide.

(46) _Melania sanctæ annæ._ (Plate XXXVII. figs. 5, 5 _a_.) Shell
small, acuminately pyramidal, somewhat eroded towards the apex,
covered with a yellowish-olive epidermis, and sometimes marked with
a few indistinct, reddish, irregular spots, and lines near the
middle of the body-whorl. Whorls 5-6 remaining, flattish at the
sides, divided by a slightly, oblique, distinct suture, all with the
exception of the last one or two more or less distinctly,
longitudinally, finely plicate; the plicæ are more conspicuous in
some specimens than in others, being at times entirely eroded. The
other sculpture consists of fine lines of growth, and a few rather
distant spiral striæ, which cut across the incremental lines and
produce a puckered appearance. Aperture elongate, pyriform, pale
bluish within. Length of specimen consisting of six whorls 13
millim., diameter 5; aperture 5 long and 2½ wide.

(47) _Melania guppyi._ (Plate XXXVII. figs. 6, 6 _a_.) Shell
slenderly acuminate, covered with an olive-brown epidermis. Whorls
about 14, divided by a very oblique, deepish suture, concave above
the middle and somewhat convex below it, and then contracted;
ornamented with a few spiral series of nodules (about five on the
upper whorls) and rather indistinct, very oblique and flexuous,
longitudinal ridges, upon which the nodules rests, also exhibiting
very sloping and flexuous lines of growth; the most conspicuous rows
of granules are near the middle of the whorls. Aperture pyriform.
Outer lip thin, remarkably sinuated above towards the suture, and
arcuately prominent below. Columellar margin oblique, straightish,
covered with a callus, curving into the broad basal sinus. Length 31
millim., diameter 7; aperture 9 long, 4 wide.

This is a very remarkable and distinct species, with a very
drawn-out spire, peculiar granuled sculpture, and a deeply sinuated
labrum. I have much pleasure in naming it after Mr. Guppy.

(66) _Unio guppyi._ (Plate XXXVII. figs. 8-8 _b_.) Shell elongate,
very inequilateral, usually a little longer than twice the height,
compressed, covered with a blackish-brown epidermis, exhibiting
strong lines of growth, and very faint radiating substriation, and
marked with fine wrinklings at the eroded beaks, which are small and
placed quite near the anterior extremity. Dorsal margin behind the
umbones almost straight or the least excurved for some distance,
then at an obtuse angle becoming oblique before rounding into the
extremity, which is a little more sharply curved than the anterior
end. Ventral outline either faintly excurved, straight, or the least
concave. Interior bluish-white, most iridescent at the hinder
extremity, generally stained in parts with olive-brown. Cardinal
tooth of the right valve moderately large, four or five-lobed at the
top, situated just in front of umbo. Between it and the outer margin
is a short ridge, the space between the tooth and the ridge
receiving the single, smaller, roughened, and striated tooth of the
left valve. Lateral tooth of the right valve long, obliquely
truncate behind, fitting in between two teeth in the opposite valve.
Anterior adductor scar deep, posterior superficial, squarish in
front. Pedal scar in both valves under the cardinal tooth very deep.
Ligament elongate, prominent.

Length 80 mm.; height 38; diameter 21.
„ 70 mm.; „ 35; „ 18.

This species recalls to mind some of the forms from Australia and
New Zealand. Its principal features are the elongate compressed
form, dark brown colour, wrinkled apices, and coarse incremental
lines. It is the only species as yet recorded from the Solomon
Islands.

ADDITIONAL NOTE. (H. B. GUPPY.)

A species of the _Litoritinidæ (Littorina scabra)_ is commonly found in this group on the leaves and trunks of mangroves, Barringtonias, and other littoral trees, the branches of which overspread the rising tide. These molluscs occur at heights varying from one or two feet to eight or nine feet above the high-water level; and they possess an unusually delicate operculum as compared with those of other species of the same family. They do not seem to be able to withstand immersion in salt water for any length of time, since out of six individuals kept submerged for twenty-four hours, three died. When first placed in the water, they were evidently very much out of their element, and tried in vain to creep out of the vessel. The delicate character of the operculum indicates a transitional stage between marine and terrestrial molluscs; and the experiment above referred to, throws a little light on this subject, since only the younger of the six individuals survived. One would have expected that the younger individuals would have been less able to withstand immersion in sea-water, but such was not the case, since they recovered from an immersion which killed the older individuals. In explanation of this unexpected result, I would infer that, on the theory of the inheritance of peculiarities at corresponding ages, the younger individuals would retain more of the marine habits of the original parent of the species, because in the first place only the adults of this parent species would have been modified to suit the new condition.