1S75.] Gr. & H. Nevill — Descriptions of new Marine Mollusca. 101 



deeply channelled at base, within showing the transverse striation on the 

 back of the last whorl ; outer lip produced, rounded, no sign of any emargi- 

 nation at the upper part, much thickened, transversely striated, with a sub- 

 granulose appearance, crenulated at the margin. 



Long. max. 3, diam. max. 1\ mil. 



Mauritius ; not uncommon in sand. 



This should probably constitute a distinct sub-genus of Rissoina, dis- 

 tinguished by the very distinct canal, twisted columella and sinistral apex ; 

 a shell dredged in Japan by A. Adams and distributed by him as " Lachesis, 

 n. sp." is a very closely allied species. 



Cyclostrema ebttrnea, n. sp., PI. VIII, Figs. 21 — 22. 



Shell depressedly orbicular, thick and callous, ivory white and shining, 

 suture distinct ; whorls 5, sharply angled a little below the centre ; longi- 

 tudinally obliquely plicated, ribs very massive, slightly wider than their 

 interstices, obsoletely granulated at the angulation ; interstices transversely 

 very closely, beautifully and regularly striated, old specimens (as the figured 

 type) are very callous and the transverse striation becomes almost obsolete ; 

 a very prominent, thick, transverse, rounded keel at the periphery, sculp- 

 tured like the whorls ; f of the base sculptured as above, the transverse 

 striation being however more distinct, the remaining f round the um- 

 bilicus is smooth, the sculpture becoming abruptly obsolete ; umbilicus mo- 

 derate, in old specimens partly covered by the thickened columella, aperture 

 irregularly rounded, margins callous and thickened, slightly reflected over 

 the umbilicus, giving a notched appearance to the columellar margin. 



Alt. 2-f-> diam. 4f mil. 



Pooree, in the Bay of Bengal. Pare. 



This handsome species is like no species of the genus as yet described ; 

 it perhaps most resembles the West Indian cancellata of Marryat, and it is 

 possible that the specimens from the Philippines recorded in the Thesaurus 

 under that name may prove to belong to our species. 



ElNGICULA ACUTA, Phil. 



Mai. Zeits. 1849, {Aden). 

 R. minuta, H. Ad., (Suez). 



Both var. minuta and the larger typical form are extremely common at 

 Aden, in the Gulf of Oman, and at Grwadar on the coast of Persia, as also at 

 Bombay, Ceylon, and Arakan ; an allied form (if not the same) was also ob- 

 tained by one of us at Natal ; the largest adult specimen in the Museum 

 measures long. 4|, diam. 3 mil., the smallest long. If, diam. 1 mil. ; there 

 are also numerous full-grown specimens of many intermediate sizes. Curi- 

 ously enough, Dr. Stoliczka obtained this species at Singapore, but not S. 

 Caron, Hinds. Dr. Armstrong has presented to the Museum a single speci- 



