62 CRETACEOUS GASTROPODA 
genera to be admitted, that it appears best to treat the fossil forms under the 
more general terms Cassis, Cussidaria (sensu Lamarcki) and Oniscia, Sowerby. 
This course is also strongly advocated by Deshayes in his last contribution to the 
Paris fossils (Tom. IIT, pp. 471, &c.), and it may at present do well enough for 
the fossil forms; although there can be no question, that some system of classification, 
of the recent species of Cassis and Cassidaria, as proposed by H. and A. Adams, 
Gray and others, must be adopted, as otherwise it would certainly be impossible to 
give a strict definition of the group. Chenu, Gray and others add Pachybatron, 
Gask. and Cythara, Shuhm. to this family; the latter genus seems to be, however, 
more properly placed in the family Pzrzvrorour.s, as will be found stated more 
fully hereafter. 
The number of fossil species of Oasszpripa is not very large in the tertiary 
deposits (see Deshayes, Tom. IIT, pp. 474 and 482), and in the secondary, it is very 
limited. The Cassis corallina, Quenstedt, from the Nattheim coral-rag having been 
proved by Dr. Rolle to belong to the family of Cozrvmezzzipx and separated as a 
distinct genus under the name of Colwmbellaria (see the family CozumeErzip2), 
the earliest true representatives of the Cassrprpm are met with in the cretaceous 
deposits. Of Cassis no cretaceous species has been as yet reported. Of the section 
Cassidaria three species are known, C. eretacea, Miler (Monog. d. Petref. d. 
Aachner Kreide, 1851, I pt., p.17, Pl. II, Fig. 21); Morio tuberculatus, Gabb. (Pal. 
Calif. 1864, I. p. 104, P1.19, Fig. 57); and Sconsia Alabamensis, Gabb (Jour. Acad. Phil. 
1860, IV, p. 801, Pl. 48, Fig. 18). This last named species is doubtful, but the two 
other appear to be true Cassidarie. Of Oniscia we have to notice the first cretaceous 
species described. It has heen found represented in a comparatively well preserved 
specimen, so as to leave little doubt as to its generic determination, and in beds 
attributed by Mr. H. Blanford to the highest division of the South Indian cretaceous 
deposits. 
IX. ONISCIA, Sowerby, 1825. 
The principal character of this genus, as distinctive from the Cassidarie, lies in 
the granulation of the thickened inner lp. It is hardly necessary to say, that the 
scarcely known name of Bolten, Morwm, cannot compete with the universally known 
Oniscia, nor do I see any particular use in distinguishing the genera (Oniscia and 
Morum, Gray; Morwn and subgenus Oniscidia, Adams and Chenu.) The difference 
between Oniscia and Morum, as stated by Gray (Guide, 1857, p. 70) reduces itself 
respectively to a plaited or denticulated outer lip, the limit of which character 
varies with the age of shells of one and the same species. I can scarcely believe, 
that the animals could show any such essential difference as to support the necessity 
for two genera. ‘The cretaceous species, which we refer to this genus, has the same 
form and a granulated thickened inner lip like other Oniscie. The canal is produced 
and recurved, the outer lip reflexed and rounded with a thickened margin -exteriorly 
as in Oniscia proper (according to Gray), but it is toothed internally, as in Morwm 
(apud Gray). 
