183 



jecting ; small cardinal teeth, varying in their number, 

 sometimes none ; the ligament external. Recent and 



fossil. — PI. vii. fig. 24. 



2. PanopcBa. — A transverse, equivalved bivalve, gaping 

 unequally at the sides ; one conical hinge tooth in each 

 valve, with a short, compressed, ascending callosity ; the 

 ligament external, fixed to the callosities on the longer side 

 of the shell. 



3 Glycimeris. — A transverse bivalve, gaping very much 

 on each side; the hinge callous, without teeth; nymphae 

 projecting outwardly ; the ligament external. Recent 



and fossil. — PL vi. fig. 27. 



MyaricB. — Bivalves ; inequilateral and subequivalved ; a 

 spoon-formed tooth on one or both valves, giving attachment 

 to the ligament ; the shell gaping at one or both extremities. 



1. Mya, — A transverse bivalve, gaping at both sides; 

 one large, compressed, and dilated roundish cardinal tooth, 

 to which the ligament is attached, projects almost vertically, 

 and, when the valves close, lies upon the ligamental pit of 

 the other valve. Recent and fossil. — PI. vii. fig. 16. 



2. Anatina, — A transverse, subequivalved, gaping bi- 

 valve, with a flat spoon-shaped tooth on each valve ; with, 

 sometimes, a falcated plate running obliquely beneath the 

 hinge teeth. Recent. 



Mactracece. — Equivalved bivalves; generally gaping at 

 the lateral extremities ; the ligament internal, with or with- 

 out a complication with the external ligament. 



1. Lutraria. — An inequilateral bivalve, transversely 

 oblong or rounded, gaping at the lateral extremities ; the 

 hinge with one tooth as if plaited into two ; or two teeth, 

 one of which is simple; with an adjoining oblique, deltoidal 

 pit, internally projecting ; no lateral teeth ; ligament internal. 

 Recent and fossil. — PI. vii. fig. 29. 



