174 EOCENE MOLLUSCA. 
An aged specimenin Mr. Edwards’s cabinet appears to correspond with the one figured 
by M. Deshayes, as above referred to. It is covered with very close-set fimbriz, which 
appear to be its principal distinction. The radiating lines are nearly obliterated by the 
numerous ridges, and from its thickness the valve has afforded a retreat for a Gastrochena. 
Our specimen is the upper or right valve. 
3. Cuama Gicas, Deshayes. Pl. XXV, fig. 2. 
Cuama cieas, Desh. Coq. Foss. des Env. de Par., vol. i, p. 245, pl. xxxvii, figs. 
5, 6, 1825. 
— — J.Sow. In Dixon’s Geol. of Suss., p. 93, pl. ii, fig. 96, and pl. iii, 
fig. 26, 1850. 
— — Desh. An. sans Vert. du Bass. de Par., vol. i, p. 581, 1858. 
Spec. Char. “ C. Testé ovato-rotundata, gibbosd, crassa, foliaced, levigatdé ; lamellis 
numerosis, concentricis, latis, irregulariter sectis; dente cardinali magno,  sulcato.” 
(Deshayes.) 
Shell roundedly ovate, gibbous or irregularly tumid, thick and strong, covered with 
foliaceous and reflected lines of growth, with protuberant short spines ; interspaces between 
lamellae irregularly distant ; cardinal tooth large and sulcated. 
Diameter, 24 inches. 
Localities. Bracklesham, Bramshaw Brook, Huntingbridge, Stubbington (dwards). 
France: Calc. gross., Parnes, Chaumont, &c. (Deshayes). 
This species does not appear to be abundant, especially of the size of the specimen 
figured, although it is stated by M. Deshayes to have been found much larger in France. 
The name gigas is retained for this species, though by no means an appropriate one. 
Chama gigas, Linné, is a very different shell, and was appropriately applied to the largest 
species in the class Bivalvia, now known under the generic name of 7ridacaa. 
Our present species seems to have adhered by its entire side when young, and occa- 
sionally so till nearly full grown. This attachment is by the anterior or pedal region. 
Fig. 3 is, perhaps, the young state of this species, resembling the shell called papyracea, 
and fig. 4 represents a specimen which, from its strong adherence, had produced a 
prominent ridge of reflected fimbriz, like plicatella. ‘These, I think, are only varieties of 
gyas. Although this genus stands pretty well isolated, there is a more than common 
difficulty in pointing out what are presumed to be their specific differences. 
