392 CRETACEOUS GASTROPODA 
4, Rimula, Defr., 1824. Shell cup-shaped, generally cancellated, apex 
incurved, subspiral, posterior, with an elongated, median perforation in front, 
situated about equally distant between the margin and the apex. Species of this 
genus are known from the Trias upwards, but they are always rare; from cretaceous 
deposits none have as yet been reported; of living species there are five or six 
known. 
4a. Oranopsis, Adams, 1860 (Ann. mag. nat. hist., V, p. 302), only differs 
from the former genus in having an “internal vaulted chamber over the foramen,” 
resembling that of Puncturella (or Cemoria). Cr. pelex, Adams, from the China seas 
is the type, and the same author has since described one or two additional species, 
also from the eastern seas. 
4b. Puncturella, Lowe, 1827 (Cemoria, Leach, teste Gray and Swainson, 
1840), in form and ornamentation resembles Limula and Cranopsis, but has the 
foramen placed in front near the apex, “vaulted over internally with a shelly 
plate.” At present only about eight or ten recent, and a few fossil, species from 
tertiary deposits have been reported. 
5, Fissurella, Bruguiere, 1789; shell cup-shaped, with the apex truncate and a 
foramen in front of it, internally surrounded by a thickened margin. The young . 
shells are said to have the apex entire and sub-spiral. 
There have been several forms distinguished by separate names, as— 
5a. Cremides, H. and A. Adams, 1854, having a rough, cancellated and 
strongly ribbed upper surface. 
5b. Fisswridea, Swains., 1840, is distinguished by a depressed, narrow form 
and an apex close to the posterior margin. 
5c. Lucapina, Gray, 1840, includes the cancellated species with a crenulated 
margin of the aperture, and the perforation surrounded by a-somewhat more thick- 
ened edge, than is usually the case in typical Fissurelle. The animal of Lucapina 
has the mantle large, partially covering the shell. I do not think that the 
crenulation of the margins can be considered as having a generic value, for it is 
quite clear that the ribbed species mus¢ have crenulated margin, otherwise the ribs 
could not be formed, and it is only by the occasional development of an internal 
thickened layer that the crenulation of the extreme margin becomes obliterate. 
5d. Gilyphis, Carp., 1856. (Capiluna, Gray, 1857, Guide, p. 166). This was 
proposed for Fiss. Cuvieri, the shell of which does not differ from the last, but 
the mantle of the animal is not so much expanded, covering only the outer edge 
of the shell. 
5e. Clipidella, Swains., 1840. Shell rather depressed, surface cancellated, 
anteriorly truncate or slightly emarginated, perforation usually somewhat anterior. 
The animal has a rather thick, tuberculated foot, provided on the sides of the front 
part with a few short filaments ; the edge of mantle is double, crenated and 
partially covering the shell. 
5 f. Fissurellidea, d’Orb., 1840. Shell depressed, nearly smooth, foramen 
large, elongated, nearly central. The animal has the mantle largely developed, 
