462 
CONCHIFERA. 
sides slightly gaping; beaks prominent; one primary compressed 
tooth in each valve, and an adjacent heart-shaped cavity; two 
lateral compressed teeth, situated near the hinge, and inserted; 
ligament internal and placed in the pit of the hinge. 
Mcictra truncata. — The Truncated Mactra. 
Plate XCI. fig. 3. 
Strong, opaque, white ; truncated on both sides ; with a few 
concentric wrinkles. One inch and a half long. Inhabits the 
British coasts. 
Genus 55—MACTRINA.— Brown. 
Generic Character. — Subtriangular, inequilateral; umbo pro¬ 
minent and obtuse ; left valve having a strong triangular, slightly 
bifid tooth ; with triangular transverse pits on each side, for 
the reception of two small depressed lateral teeth in the oppo¬ 
site valve, and a triangular pit between them; ligament ex¬ 
ternal. 
Mactrina triangularis _ The Triangular Mactrina. 
Plate XCI. fig. 30. 
Strong, opaque, white; inside white, not very glossy ; margin 
strongly crenated. Length, one eighth of an inch. Inhabits 
the sea on the Dorsetshire and Kentish coasts. 
Genus 56.—LUTRARIA— Lamarck. 
Generic Character. —Inequilateral, transversely oblong, or 
rounded, gaping at the extremities ; hinge with one tooth, which 
is somewhat complicated, or two teeth of which one of them 
is simple, with an adjoining deltoid hollow, which is oblique, 
and prominent within ; no lateral teeth ; ligament internal; at¬ 
tached in a pit. 
Lutraria elliptica. — The Oval Lutraria. 
Plate XCI. fig. 4. 
Oblong-oval, nearly smooth, having a few concentric, nearly 
obsolete wrinkles ; and some diagonal striae at the ends of the 
valves; of a fine yellow, or greenish-brown; inside white. 
Five inches broad. Inhabits the seas of Europe. 
