OF SOUTHERN INDIA. 267 



and the position of the cartilage is not known. A. Adams believes that the genus 

 belongs to the Las^id.e, = Ertcinid^. 



The only cretaceous species known is Erychia ( KelUa) cretacea. Con., Journ. 

 Acad. N. Sc] Ph., iv, p. 280, pi. iG, fig. 19. 



XXVI. Family,— GAL.E0M3IID^E. 



The form of the animals is elongately ovate or sub-orbicular; they possess a 

 thick, united mantle with a comparatively small anterior and posterior opening, the 

 first consisting of a simple mantle-fold above the gape for the foot, the second of a 

 short exhalant tube ; the external edges of the mantle project beyond the margins 

 of the shell ; there are as usually two pairs of gills and two of labial palps ; the 

 foot is elongated and byssiferous. 



The shells are small, very thin, always more or less gaping, hinge very small, 

 with obsolete or nearly obsolete teeth and an internal cartilage. 



To this family belong the following five genera, Lihmtula, Scintilla, Fassya, 

 Oaleomma, and Thijyeopsis. They form a natural group by themselves, differing 

 from the ERTCimBM by the very thin gaping valves and by having the mantle 

 margins much more united than the animals of the last named family. About 50 

 recent species have been described, but only a few tertiary, and none from mesozoic 

 or older deposits. 



1. Libratula, Pease, 1865, (Proc. Zool. Soc, Loud., p. 512). Semi-lunar, 

 much compressed, (like a Placuna), slightly gaping all round, cardinal margin 

 crenulated, cartilage median, internal; type, L. plana, from the Pacific islands, 

 found on coral. 



2. Scintilla, Desh., 1855, (Proc. Zool. Soc, Lond., p. 171, and Paris foss., 2nd 

 ed., i, p. 697). Oval, equilateral, sometimes slightly gaping, hinge not emarginated 

 in the middle, with one uncinate cardinal tooth in the right and two in the left 

 valve, a posterior lateral tooth single in the right and double in the left valve, 

 anterior lateral margin internally grooved in both valves ; cartilage in a groove in 

 front of the posterior lateral teeth; type, Sc. Philippinarum, Desh. 



Deshayes describes no less than thirty-six recent species from Cuming's collec- 

 tion, some of them rather difficult to be made out again. A few additions to that 

 number have been made since by Sowerby and others. Two species are also noted 

 by Deshayes from the Paris basin. 



3. Fassya, Desh., 1860, (Paris foss., 2nd ed., i, p. 688). Elongated, sub- 

 triangular, somewhat irregularly rounded in front, produced behind, very inequi- 

 lateral, with an almost straight and very long upper margin, gaping at both ends, 

 hinge sub-anterior, with a small tubercular tooth in each valve ; ligament internal ? 

 muscular scars very small, remote; type, P. Ewjenii, Desh., from eocene beds of 

 the Paris basin. In the single species as yet known the position of the car- 

 tilage has not been observed, but in general character of structure, and especially 

 in the peculiar gaping, the shell resembles the next genus. 



3 u 



