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estuaries: Littorina melanostoma also occasionally occurs, but its home is nearer the sea.

Lower down where the creeks are broader, the belt of salt swamp is narrower in general, and a broad shelving muddy shore succeeds, the upper portion covered by a thick forest of Avicensia, while lower down Nipa palms frequently occur. The beauty of the wide creeks is greatly enhanced by the broad fringe of the bright green Avicensia, over the tops of which the summits of hills, covered with dense green forest, are frequently visible. On the sloping muddy shore species of Potamides, Assiminia, Amphibola, Plecotrema, Haminea, Stenothyra; Arca granosa, Nassa planicostata, and Columbella Duclosiana are to be met with. On the stems of the Nipa and on the mangrove bushes Neritina crepidularia and N. cornucopia, Littorina melanostoma and L. scabra are found in abundance.

I have only included in the present list those shells from the Bassein river which are found above Negrais Island, for the reasons already stated. I regret that the list is not more perfect, and that I am obliged to leave a few specimens undetermined. On the other hand the majority have been carefully compared, and the names quoted may, I think, in most cases, be relied upon. Immediately after leaving Pegu, I was in England for a few months; and owing to the kindness of the late Mr. S. P. Woodward, of Mr. Arthur Adams, and especially of the late Mr. Hugh Cuming, who allowed me to compare my shells with the original types in his unrivalled cabinet, I was enabled to determine, not merely my estuary collections, but also a much more numerous series of marine species from the Arakan coast, in a manner which would have been simply impossible in India.

Unfortunately, during the years which have elapsed since these shells were compared, a few have been mislaid or lost during constant travelling in various parts of India. Still I hope that this list may have some value as a contribution to our knowledge both of the geographical distribution and of the habitats of mollusca. Several of the species named, and some of the genera have, so far as I am aware, never before

So great is the height of the trees fringing the upper creeks, and so completely do they shut out all the surrounding country, that I was working amongst them for several days in ignorance of the existence of hills nearly 1000 feet high within 15 or 20 miles of me.

been shewn to inhabit the estuaries of India or Burma. Our estuary lists have hitherto been almost as imperfect as our catalogues of marine species; almost all that is known of the molluscan inhabitants of our deltas being due to the labours of Mr. Benson, who has described many of the forms found in the Ganges.

It is, of course, highly improbable that the present list is nearly complete. Only a very small portion of the Irawadi delta was examined, and that imperfectly. Still the number of species is considerable, and probably includes all those which are most abundant. A few forms since found by Mr. Theobald and Mr. Fedden will be noted in their place.

The classification employed is mainly that of Messrs. H. and A. Adams, in the Genera of Recent Mollusca. I have not, however, followed those authors in employing the obscure and forgotten generic terms of Klein, Montfort and others I have only deviated from their arrangement in one essential particular, viz., the transfer of Assiminia from the vicinity of Helix, from which it differs in every point of structure, to that of Littorina, to which it is closely allied. If it be objected that Assiminia is as closely related to Cyclostoma as it is to Littorina, I can only suggest that Cyclostoma be also relegated to the same position in the neighbourhood of Littorina.

Class GASTEROPODA.

Sub-class PROSOBRANCHIATA.

Family BUCCINIDE.

No. 1, Nassa planicostata, A. Adams.

Estuary of the Bassein river, creeping upon mud between tidemarks. Scarce.

No. 2, Purpura bitubercularis, Lam.

Not common. Found in the lower part of the delta, with the next species.

Family MITRIDEÆ.

No. 3, Columbella Ducloziana, Sow.

Found in abundance at one spot in the estuary of the Bassein river, amongst stones with mud. The specimens were unusually fine. I also met with this shell on the mud flats of Ramri Island, coast of Arakan.

Family SCALARIADÆ (Scalidæ, H. and A. Adams.) No. 4, Scalaria, sp.

A minute species, apparently new. As I possess but a solitary specimen, which is not in the best possible order, I hesitate to describe it. It is one of the smallest forms known, measuring only 3 millimetres in length. It was found under stones in the Myittaya creek.

Family CERITHIIDÆ.

No. 5, Cerithium (Vertagus) obeliscus, Born.
A single specimen was found at Port Dalhousie.
No. 6, Potamides (Tympanotonos) alatus, Phil.

No. 7, Potamides (Tympanotonos) euriptera, A. Ad.

Both this and the last species are met with abundantly on mud between tide marks, not far from the sea. They also occur on the sea coast where it is muddy.

No. 8, Potamides (Telescopium) fuscus, Chemn.

Common on mud between tidemarks, where the water is completely salt.

Besides the above, a species of Cerithidea has been found by Mr. Theobald in the estuaries of Burma. I did not meet with it.

Family LITTORINIDÆ.

No. 9, Littorina melanostoma, Gray.

Very abundant upon "mangrove" trees, close to high water mark. No. 10, L. scabra, L.

Occurs with the last, which appears to pass into it. Two varieties of this form occur, one more coarsely sculptured and more stoutly keeled than the other.

No. 11, L. zic-zac, Chemn.

Syn. L. undulata, Gray.

This species is frequently found on the sea coast, especially near mouths of rivers. In the estuary of the Bassein river, it occurs together with true estuarine forms. It is met with on stones and dead wood, close to high water mark.

Family ASSIMINIIDE.

No. 12, Assiminia rubella, W. Blanf. pl. II. fig. 11. 12.

A small roundly ovate, dull red species, which occurs abundantly

near Port Dalhousie, on mud between tidemarks. It is a characteristic Assiminia, though much shorter and rounder than the Bengal species A. Francesi, Gray, and belonging in fact to a different section of the genus. It is closely allied to some Singapore species and also to A. marginata, Leith, which inhabits Bombay, but may be distinguished from all by the double marginal impressed line below the suture.

The animal is deep red, with a black spot upon each of the lobes into which the proboscis is divided. The eyes are at the top of the short tentacles.

Family RISSOIDÆ.

IRAVADIA, n. g.

Testa imperforata, turrita, spiraliter costata, solida, epidermide tecta : apertura ovata, integra, antice obsolete effusa; peristomate recto, extus variciformi-incrassato, intus dilatato.

Animal? Operculum?

Shell imperforate, turrited, spirally ribbed, rather thick, covered with an epidermis. Aperture ovate, without a canal, slightly effusə in front; peristome straight, not sinuate, with an external varix, and slightly expanded within. Animal and operculum unknown. No. 13, Iravadia ornata, n. sp. Pl. II. fig. 13. 14.

Testa turrita, decollata, subcylindrica, (junior elongato-conica), solida, spiraliter costata, inter costas confertim verticaliter costulata, sub epidermide olivaceá vel ferruginea albida. Anfr. superst. 3-4, rotundati, superi tribus, penultimus quatuor, ultimus sex costis spiralibus ornati, hoe juxta aperturam paulo ascendente. Apertura sub-verticalis, elliptica, intus alba, (in testá juniori postice angulata), antice subangu lata et in testá adultá obsolete effusa, in jumori subcanaliculata ; peristoma extus incrassatum, nodoso-variciforme, nodis costis spiralibus congruentibus, intus vix expansum. Opere.?

Long. 41, diam. 21 mill.

Shell turrited, decollated (the young shell elongately conical,) thick, spirally ridged, with close vertical costulation between the ridges, white, with a brownish or olive epidermis. Whorls apparently about 6, when perfect, but only 3 or 4 remain in all the specimens collected; body whorl with 6 spiral ribs, of which 4 only appear on the penultimate whorl, and 3 on the upper whorls, the lower ribs being concealed. On all the upper whorls the 2nd and 3rd ridges are the

strongest. Those near the suture, both above and below, are less strongly marked, and are occasionally obsolete. On the last whorl the uppermost ridge near the suture is alone fainter than the others. The body whorl ascends a little towards the aperture, which is subvertical and nearly elliptical. The anterior canaliculation is obsolete in the adult, but it is well marked in the young shell. Peristome much thickened, externally variciform, the varix being nodose in consequence of the spiral ribs of the body whorl being continuous upon it. In young specimens the lip is grooved inside, the grooves corresponding to the external ribbing, and slight remains of this grooving may be traced in the adult shell.

I had at first classed this shell as a Rissoina on account of the obsolete canal, although it differs in essential characters from any species of that genus. I am indebted to my friend Dr. Stoliczka for calling my attention to the great distinctions which exist between the present form and Rissoina, and some of which equally serve to distinguish it from Rissoa and all other genera of the group. Iravadia differs from Rissoina in possessing an epidermis, in having spiral sculpture, in the peristome neither being sinuate above, nor projecting below, and in the columellar margin being simply curved in front and not excavated. From Rissoa it is distinguished also by its epidermis and sculpture, by the obsolete channel in front of the aperture, which, in young specimens, is quite as distinct as in Rissoina, and by the absence of any tendency to the columellar tooth or fold, which is so conspicuous in the typical species of the genus. The characters of the sculpture, epidermis, and aperture serve equally to separate the present form from Alvania, Onoba, Ceratia and other genera of Rissoida: Hydrobia and Amnicola alone have an epidermis, but both are smooth shells without a variciform peristome.

It is unfortunate that no specimen of the operculum has been preserved. The few shells found were collected during a hurried journey in a boat. The species was only met with at one spot, under stones, amongst some rocks in a creek leading into the Myittaya, a branch of the Bassein river. Several specimens were obtained, but when an opportunity was afforded of examining them at leisure, the opercula had disappeared. In the absence of the operculum, I should be disposed to consider the genus as more nearly allied to Rissoina than to

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