ANATINIDA. 147 
fossil Corimye. But among the enormous number of known 
Pholadomye, we meet similar variations in one and the same 
genus. 
Myvtitimeria, Conrad, 1837. 
Distr.—2 sp. M. Nuttalli, Conr. (eviii, 68). 
Shell rounded-oval, more or less ventricose, equivalve, fragile, 
covered by a thin caducous epidermis; beaks subspiral; hinge 
without teeth, but formed of small linear excavations under the 
beaks to receive the ligament, which contains a small ossicle ; 
muscular impressions small; pallial impression with an obtuse 
sinus. 
Animal gregarious, forming a nest. 
EpmonptA, Koninck, 1842. 
Distr.—Fossil, 4 sp. Carb.—Permian; Europe. J. unioni- 
formis, Phil. (evii, 39). 
Shell oblong, equivalve, thin, concentrically striated, close ; 
umbones anterior; ligamental grooves narrow, external; hinge- 
line thin, edentulous, furnished with large oblique cartilage- 
plates, placed beneath the umbones, and Jeaving space for an 
ossicle ? or the plate may be equivalent to the subumbonal blade 
in Pholas; pallial line simple ? 
CarpiomorPHA, Koninck, 1842. 
Distr.—Fossil, 38 sp. Lower Silurian—Carb.; N. America, 
Europe. C. excentrica, Agass. (cvii, 40). 
Type, C. oblonga (Isocardia), Sowerby (not Koninck). Car- 
boniferous. 
Shell Isocardia-shaped, smooth or concentrically furrowed, 
umbones prominent, hinge edentulous; hinge-margin with a 
narrow ligamental furrow, and an obscure internal cartilage- 
groove. 
Crromya, Agassiz, 1842. 
Etym.— Keraos, horned ; mya, mussel. 
Distr.—Fossil, 14 sp. Inferior Oolite, Greensand ; Europe. 
C. Aalensis, Quenst. (evii, 41, 42). 
Shell Isocardia-shaped, slightly inequivalve? very thin, gran- 
ulated, often excentrically furrowed ; ligament external; hinge 
edentulous; right valve with an internal lamina behind the 
umbo; pallial line scarcely sinuated ? 
The Ceromye are principally characterized by their tumid, thin 
and concentrically laminated shell, distant beaks, and the oblique 
furrows which are externally traceable. Chenu unites this to 
Cardiomorpha, but in that genus there does not appear to be 
any such arrangement for the attachment of an internal liga- 
ment (similar to that of Lyonsia); there is along the raised 
