254 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 



FAMILY VI. VENERINA. 



Animal orbicular, roundish, ovate, or oblong, more or 

 less compressed ; with the mantle-lobes free beneath, 

 united behind to form a tube containing two siphons ; 

 a compressed, extensile foot ; two roundish, widely se- 

 parated adductor muscles. 



Shell orbicular, roundish, ovate, or oblong, generally 

 convex, subcordate, thick, concentrically striate, seldom 

 with an epidermis ; the umbones prominent, approxi- 

 mated ; the hinge with from two to four divergent strong 

 teeth, and elongated lateral teeth ; the 1-gament external, 

 prominent ; anterior slope with a cordate or ovate im- 

 pression. 



All the species marine. 



GESUS 1. LUCINA. 



Animal orbicular, compressed ; the margins of the 

 mantle fringed ; the foot elongated, cylindrical ; tubes 

 short, united in their whole length, and entering into a 

 replication of the mantle. 



Shell suborbicular, subinequilateral, concentrically 

 striated. Umbones small, oblique, rather pointed. 

 Hinge variable, generally the right valve with two diver- 

 gent, moderately prominent teeth, leaving between them 

 a triangular depression; toward the posterior border 

 under the ligament an elongated little-elevated lamina, 

 succeeded by a shallow groove, and along the anterior 

 margin a slight ridge ; the left valve with two divergent 

 teeth, and an intermediate depression, an elongated 

 ridge along the posterior margin, and a shallow groove 

 along the anterior. Muscular impressions widely sepa- 

 rated, the anterior generally with a narrow prolongation. 

 Pallial impression entire. Ligament external and rather 

 elongated. 



There seems no reason for separating Lucina and 

 Loripes. It will however be obvious to any one who 

 compares the shells of any true Lucina with that of 

 "Lucina undata," that this latter, having the pallia! 



