48 



The two muscular impressions are situated on each side of the in- 

 terior a little below the summit ; while, in Patella, they nearly 

 surround the internal circumference of the same part of the shell. 

 The aperture is generally surrounded by a margin, and the apex, 

 which in Ancylus is oblique, is central though posterior. 



Mr. Cuming brought home the following species which I now pro- 

 ceed to describe. 



ScuTELLA CRENULATA. Scut. testd subcouicd, concelUitd, striis ah 

 apice radiantibus exasperatis, albd; intiXs nitente ; annulo mar- 

 ginali et margine crenulalis : long, f , lat. ^, alt. -rV poll. 



Hab. ad insulam Anaan (Chain Island), 



This shell was found dead on coral sand on the beach of the island 

 at a distance from any fresh water. 



The marginal ring is very strongly developed, and the margin it- 

 self is not even ; for when the shell is placed with the aperture down- 

 wards on a fiat surface, it rests on the two ends> the sides of the 

 margin forming each a low arch. 



ScuTELLA iRiuESCENS. Scut. testd oblougO'Ovatd, complauatd, mi- 

 nutissime substriatd, albo et rosea guttatim tessellatd ; intus iri- 

 descente, margine interno albo, roseomaculato : long. -r\, lat^ i^, 

 alt. -rV poll. 

 Hab. in Oceano Pacifico. (Grimwood's Island.) 

 This species was gathered by Mr. Cuming on the sands when the 

 tide was out. There was no fresh water near, and though he obtained 

 several individuals in the finest condition, the soft parts were gone, 

 having evidently but lately fallen a prey to some carnivorous crea- 

 ture. 



The shape of Scut, iridescens is very elegant, and the silvery iri- 

 descent nacre which lines the inside of the shell, contrasted- as it is 

 with the less brilliant but lively coloured margin, is almost dazzling. 

 The back of the shell, which is very brittle, is mottled with white and 

 rose colour. This disposition of its markings almost conveys the im- 

 pression that the surface of the back is uneven ; but with the excep- 

 tion of the very minute strice, which are almost imperceptible, it is 

 smooth. 



ScuTELLA ROSEA. Scut. testd' xubcouicd , siriatd, albd, lineisjlam- 

 mulisque roseis ornatd; intiis nitente, interdum suhiridescente : 

 long. -J-, lat. iV, alt, tV poll. 



Obs. Varietas forsan prsecedentis, 



Hab. cum praecedente. 



The shape and many other points in this shell differ from those of 

 Scut, iridescens. Externally it is much more conical and the strite 

 which run from the apex to the interior margin are direct and minute, 

 while those which are lateral are much coarser and cross the some- 

 what elevated white parts obliquely: in Scut, iridescens, the exceed- 

 ingly minute strice radiate evenly from the apex. In Scut, rosea we 

 lose the brilliancy of the internal nacre which distinguishes Scut, 

 iridescens, and, in some individuals, it is entirely absent. Still the 



