140 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
Pl. CCII. Fig. 6. (fossil.) 
NERITA TRICARINATA, Lamarck, Anim. sans vert., new edit., vol. villi. 
p-616. Ann. du Mus., vol. v. p. 94; and vol. viii. pl. 62. f. 4. a, b. 
Deshayes, Coq. Foss. de Paris, vol. il. p. 160. pl. 19. f. 9 and 10. 
NERITOPSIS, Sowerby. 
Testa obovata, exttis granosa, anfractibus paucis, rapidé crescentibus, 
spira brevi, apice subelato, acuto; apertura transversa, subsemilu- 
nari, marginibus disjunctis ; labro incrassato, fauce tenuiter sulcata ; 
columella solida, propé ad medium laté emarginata. Operculum 
tenue, corneum, non spirale. 
The genus Neritupsis was introduced by Sowerby for the sake of distin- 
guishing a delicate cancellated shell, that was known to Linnzus, Born, 
Chemnitz and others of their day as the Nerita radula*. The Neritopses, 
* We cannot but appreciate this excellent genus, as founded by Sowerby upon the shell 
which is given in his ‘ Genera’ in illustration of it; but he is mistaken in supposing it to be 
the Sigaretus cancellatus of Lamarck, Nerita cancellata of Chemnitz: both shells are now before 
us, and we therefore hasten without diffidence to correct the inaccuracy. It is not surprising 
that they should have been figured and described by Chemnitz under the same generic title, 
for his Nerite radula and cancellata, the shells in question, are not unlike in colour and general 
form ; but a very slight examination would have shown him that whilst the former, Neritopsis, 
is rather a solid shell, granulated on the outside upon ribs running longitudinally, independent 
of the peculiar formation of the columella, the latter is thin, light, ventricose, and cancel- 
lated in ribs running in a transverse direction. But of their animal inhabitants ?—we know 
nothing certainly of the first of these, yet, upon looking at its shell, can fairly trace an affi- 
nity between the Neritopsis and the Nerite by analegy; the second, however, which was 
removed by Lamarck to a place amongst the Sigareti, from a conviction that it presents few 
characters in common with the Nerite, is, in reality, allied to the Velutine. We are indebted 
to M. Quoy for both a figure and description of this mollusk in his ‘ Zoologie’ of the ‘ Voy- 
age de l’Astrolabe,’ under the title of Velutina cancellata; although it is referred to that 
genus, he nevertheless suggests that it might be set apart for the formation of a new one, 
