CONCHIFERA. 
ANISODONTA, Deshayes, 1860. 
Type, A. conplanatum, Dh. Eocene. Paris basin. 
Shell transversely elongated, compressed, inequilateral ; hinge 
thick; a large conical and a triangular socket in each valve; 
ligament external. Anterior adductor scar very small, and 
comprised between two prominent ribs (one parallel and the 
other transverse to the anterior border); posterior scar subcir- 
cular, superficial; pallial line faint, entire. 
Distribution, 2 species. Bourbon. 
?P MATHERIA, Billings, 1858. 
Dedicated to Mr. Mather, of the Geological Survey of New 
York. 
Type, M. tenera, Billings. Trenton limestone, Canada. 
Shell transverse, equivalve; beaks near the anterior end; two 
small obtuse cardinal teeth in the left valye, and one in the 
right; ligament external. 
ConcHopon, Stoppani, 1865. 
Etymology, conchos, a shell, and odos, a tooth. 
Type, O. infraliasicus, Stop. Lower Lias. Lombardy. 
Shell equivalye, symmetrical, very thick, cordiform, closed; 
beaks large, angulated, involute. Ligament internal, very 
long, marginal, attached to the posterior half of the hinge-plate. 
Hinge massive; in the right valve, one large rounded tooth in 
front (placed above a dental pit), and two transverse cardinal 
teeth ; left valve with a large circular socket, bounded below 
by a curyed lamellar tooth; two transverse and one curved 
teeth beneath the umbo. 
DICEROCARDIUM, Stoppani, 1865.. _ 
Etymology, diceras, having two horns, and cardium. 
Shell equivalve, symmetrical, closed, free; umbones very 
prominent, elongated, or spiral. Hinge-plate broad, thick, 
separated by an interval of varying width from the edge of the 
valve, and prolonged into the umbonal cayity. Left valve with 
a compressed cardinal tooth, corresponding to a socket in the 
right valve; valves furrowed by igamental grooves. Ligament 
external. 
Fossil, 4 species. Upper Trias. Lombardy, North-West 
Himalayas. "5 
