CORBULIDiE. 355 



abruptly truncated on the posterior side. The recent 

 species known come from the West Coast of Africa ; fossil 

 species occur in the Miocene of Dax, and the Morea. 



Species of Tugonia. 



anatina, Gmel. semisulcata, A. Adams. 



nobilis, A. Adams. 



Fam. COEBULID.E. 



Body not symmetrical. Palpi long, narrow, pectinated on 

 both sides. Mantle closed, except anteriorly ; pedal orifice 

 small, the margins dentate ; siphons short, united, the 

 orifices fringed with cirrhi, the anal furnished with a tubu- 

 lar, membranous, retractile valve ; gills two on each side, 

 dependent, separate, moderately prolonged. Foot long, 

 sub-cylindrical, furnished with a byssal groove. 



Shell porcellanous, valves unequal, closed posteriorly. 

 Hinge with a conical tooth and a cartilage-pit in each valve. 

 Pallial line slightly sinuated. 



Genus CORBULA, Bruguiere. 



Siphons very short, united. 



Shell ovate, gibbose, closed, very inequivalve; the left valve 

 the smaller, rounded anteriorly, more or less truncate pos- 

 teriorly; beaks prominent; surface of valves more or less 

 furrowed or transversely striated, covered with an epidermis. 

 Hinge composed of a recurved prominent tooth in the right 

 valve in front of the cartilage-pit, and a projecting cartilage- 

 process in the left valve ; cartilage small, interior. Pallial 

 line with a very slight sinus ; pedal scars distinct from the 

 adductor impressions. 



