76 CONCHIFERA. MONOMYAIKA. 



pierced on its under surface with three unequal and oblique 

 holes ; upper valve very convex, furnished interiorly with two 

 projecting callosities. 



C. personala, Lam. (A. craniolaris, Gmel.) Shell orbicular ; upper 



valve conical ; lower with three holes. Inhabits Indian seas 



Chem. viii. pi. 76, fig. 687- 



Species of this genus are found fossil in France and Sweden. 



Gen, 5. DISCINA, Lam. 



Shell inequivalve, rounded, slightly depressed ; valves of equal 

 size, with each an orbicular and central disk ; disk of the up- 

 per valve not pierced, with a mammillated protuberance in 

 the middle ; the lower valve divided by an oblong fissure. 



D. ostreoides, Lain. Upper valve with five longitudinal ribs, cros- 

 sed by concentric circles. 5 lines long. Found on the British 

 coasts. Lin. Trans, xiii. pi. 26, fig. 2. 



Gen. 6. BIROSTRITES, Lam. 



Shell inequivalve, with the valves elevated and conical, oblique- 

 ly diverging, almost straight, in the form of horns, the one 

 enveloping the other at the base. (Fossil.) 



Gen. 7. CALCEOLA, Lam. 



Shell inequivalve, triangular, turbinated, flattened below, the 

 large valve hollowed like a hood, truncated obliquely at the 

 aperture ; the small valve semiorbicular, in the form of an 

 operculum, with a furrow in the centre. (Fossil.) 



Gen. 8. RADIOLITES, Lam. 



Shell inequivalve, striated exteriorly, the striae longitudinal and 

 radiated ; lower valve turbinated and largest ; the upper con- 

 vex or conical, operculiform. (Fossil.) 



The Radiolites are found only in strata of the older formation, in the Pyrenees. 



Gen. 9- SPILEHULITES, Lam. 



Shell inequivalve, orbicular, slightly depressed above, rough 

 with large subangular horizontal scales ; upper valve smallest, 

 witfrtwo tuberosities on its internal surface ; lower valve with 

 the scales radiating beyond the margin, and forming a ridge. 

 (Fossil) 



SECTION II. 



Ligament not marginal, inclosed in a short space under the 

 beak, always perceptible, and never forming a tendinous chord 

 under the shell. 



FAMILY I. OSTRACEA. 



Ligament interior or partly so ; shell irregular, foliaceous, some- 

 times papyraceous. 



Almost all the Ostracea have irregular foliaceous or lamellar shells, rarely eared 



