184 



2. Mactra. — A transverse, inequilateral, subtrigonal bi- 

 valve, a little gaping at the sides ; the beaks prominent ; a 

 compressed grooved cardinal tooth, with an adjoining pit ; 

 two lateral compressed inserted teeth ; ligament internal. 

 Recent and fossil. — PI. vii. fig. 30. 



3. Crassatella. — An inequilateral, suborbicular, or trans- 

 verse, close shell ; hinge complicated, two cardinal teeth 

 slightly diverging with a pit at the side ; ligament internal ; 

 lateral teeth, obsolete or none. Recent and fossil. — PI. viii. 

 fig. 9. 



4. Erycina. — A transverse, subinequilateral, equivalved 

 bivalve, seldom gaping ; two unequal, diverging cardinal 

 teeth, with an interposed pit ; two lateral, oblong, com- 

 pressed, short penetrating teeth ; the ligament internal. 

 Recent and fossil. — PI. viii. fig. 10. 



This is an equivocal genus ; the character of the hinge 

 being, with difficulty, ascertained. 



5. Ungulina. — A longitudinal or subtransverse bivalve, 

 nearly equilateral, and with close valves ; one short subbifid 

 cardinal tooth on each valve by the side of an oblong mar- 

 ginal pit, nearly divided in two ; the ligament internal. 

 Recent. 



6. Solemya, — An equilateral, equivalved, transversely 

 oblong bivalve ; beaks hardly distinct ; a dilated, compressed, 

 very oblique cardinal tooth in each valve, with a slight con- 

 cavity receiving the ligament. Recent. 



7. Amphidesma. — A transverse, inequilateral, suboval 

 bivalve, sometimes a little gaping at the sides ; the hinge 

 with one or two teeth, and a narrow small pit for the in- 

 ternal ligament, there being another external. 



CorbulecB, 



1. Corbula. — A regular unequivalved, inequilateral bi- 

 valve ; a hinge tooth on each valve ; conical, curved, and 



