185 



elevated, with a pit at the side ; no lateral teeth ; ligament 

 internal. Recent and fossil. PI. vii. fig. 20. 



2. Pandora. A regular, unequivalved, inequilateral, 

 transversely oblong bivalve ; the upper valve flat, with two 

 oblong obtuse teeth, the lower one convex. Recent. 



Mr. G. Sowerby considers that this shell possesses only 

 one obtuse tooth on the flat valve. 



The lithophagous shells, without tube, or accessory pieces, 

 are rounded or obtuse at the ends, more or less gaping 

 forwards, with the ligament external. They are divided, 

 by Lamarck, into three genera : 



1. Saxicava. A transverse bivalve ; hinge without teeth. 



2. Petricola. A transverse, inequilateral bivalve, nar- 

 rower in the fore part ; with two teeth on one, or on both 

 valves. PI. vii. fig. 22. 



3. Venerupis. A transverse, inequilateral shell, very 

 short in the hind part ; the hinge with two teeth on one 

 valve and three on the other, and sometimes with three on 

 each valve. 



NympJiacece. With two cardinal teeth, at the most, on 

 the same valve ; a little gaping at the lateral extremities ; 

 the ligament external ; the ligamental cartilage projecting. 



1. Sanguinolaria. A transverse subelliptical shell, 

 gaping a little at the sides ; the upper margin bowed, not 

 parallel with the lower ; the hinge with two approximated 

 teeth in each valve. Recent. PL vii. fig. 25. 



2. Psammobia. A transverse, elliptical, or oval-oblong 

 bivalve, rather flat, and a little gaping on each side ; the 

 beaks prominent ; the hinge with two teeth on the left valve, 

 and only one, penetrating, on the opposite valve. 



3. JPsammotea. A transverse, oval, or oval-oblong bi- 

 valve, a little gaping at the sides ; one cardinal tooth in one, 

 and sometimes in both, valves. 



Bb. 



