stone. The attached valves have not attained a great degree of 

 thickness, consequently I do not suppose any one of the individuals 

 to be of advanced age ; there are, however, several vi'hich can only 

 just have occupied their positions on the stone : these are not above 

 Vt part of an inch in diameter, and they show the perfect point of 

 the upper valve, somewhat convoluted and inclined toward the ante- 

 rior edge. Other individuals, which are placed in a cavity of the 

 stone, are very regular in shape, but have their ridges slightly curved 

 upwards in conformity with the nearly regular vesicular shape of the 

 cavity. The edges of the lamellce near the outer margin in most of 

 the specimens are furnished with a thin fringe of epidermis, but the 

 very young shells are destitute of this. An individual of Hipp. 

 "subriifa is observable among the group of Hipp. Mitrula: its apex is 

 distinctly spiral and its epidermis haiiy. 



" The second specimen belongs to the species which I have named 

 Hipp, bcirhata. This is a very complete specimen, and reminds me 

 of the beautiful fossil species Hipp. Cornucopia ; it is a small indivi- 

 dual, having its attached valve very much thickened and adhering to 

 a much larger one of the same species ; its edge is much elevated 

 and it is deeply concave ; the free valve is rather smaller, and coni- 

 cal, and its edge is surrounded by the elevated edge of the attached 

 valve."-G.B. S. 



~ HippONYx Mitrula. (Pileopsis Mitrula, Lam. Patella Mitrula, 

 Auct.) Hipp, testd alba, subconicd, concentric^e lamellosd, la- 

 mellis suhconfertis, radiatim striatis, epidermide pilosis. 

 Hab. ad Insulam Peruvianam Lobos dictam. 

 Found upon stones, in seventeen fathoms' water, among coarse 

 sand.— G. B. S. 



'^ HippONYX suBRUFA. (PUcopsis subrufus, Lam. Patella subrufa, 

 Dillw.) Hipp, testd aurantiaco-rufescente, subconicd, concen- 

 trice sulcatd, radiatim striatd, striis profundis, marginibus sulco- 

 rum crenulatis ; vertice postici inclinato. 

 Hab. cum praecedente. — G. B. S. 



^ HiPPONYx RADiATA, Gray. Hipp, testd subdepresso-conicd, ful- 

 vescente, radiatim costatd, costis crebris, imbricato-squamosis ; 

 vertice postico. 

 Hab. ad Panamam et ad Insulas Gallapagos. 

 Found attached to rocks alive, and the upper valves loose on the 

 sands.— G. B. S. 



HippONYx BARBATA. Hipp, tcstd palHde fulvd, subelevato-conicd, 

 radiatim confertim striatd ; margine ventrali prodvcto ; epider- 

 mide piloso-barbatd ; margine interna crenulato. 



Hab. ad Insulas Maris Pacifici. 



Found on the coral reefs around Toobouai, one of the Society 

 Islands.— G. B. S. 



