174 EOCENE MOLLUSC A. 



An aged specimen in Mr. Edwards's cabinet appears to correspond with the one figured 

 by M. Deshayes, as above referred to. It is covered with very closp-set fimbriae, 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 Gastrochcena. 

 Our specimen is the upper or right valve. 



3. Chama gigas, Deshayes. PI. XXV, fig. 2. 



Chama gigas, Besh. Coq. Foss. des Env. de Par., vol. i, p. 245, pi. xxxvii, figs. 

 5, 6, 1825. 



— — /. Sow. In Dixon's Geol. of Suss., p. 93, pi. ii, fig. 96, and pi. iii, 



fig. 26, 1850. 



— — Desk. An. sans Vert, du Bass.de Par., vol. i, p. 581, 1858. 



Sjjec. Char. " C. Testa ovato-rotundatd, gihhosd, crassd, foliaced, Icevic/atd ; lamellis 

 numerosis, concentricis, latis, irregulariter sectis ; denfe cardinali magno, sulcata " 

 {Deshages.) 



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, 2\ inches. 



Localities. Bracklesham, Bramshaw Brook, Huntingbridge, Stubbington {Edwards). 

 France: Calc. gross., Fames, 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, Linne, is a very difi"erent shell, and was appropriately applied to the largest 

 species in the class Bivalvia, now known under the generic name of Tridacna. 



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. 8 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 fimbriae, like plicatella. These, I think, are only varieties of 

 gigas. 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. 



