PELECYPODS 



441 



tropical genera as Valuta and Conus are found fossil in northern 

 Siberia seems to be evidence in proof of great climatic variations. 



A. castanea. This species has a thick and heavy shell for one so 



small, with round ventral margins and prominent beaks. The surface 



is very slightly undulated and is covered with a thick 



chestnut epidermis with pale and dark zones. The 



hinge is broad and flat, with a prominent cardinal 



tooth upon the right valve, which accurately fits into 



a pit formed by two teeth on the left valve. Length 

 one inch ; height one inch. 



A. undata. A species slightly larger 

 than the last, with ten to twenty promi- 

 nent concentric undulations. 



The identification of the many species 



of Astarte often becomes exceedingly difficult on account 

 of the fact that the genus is a remarkably uniform one in 



its main characters and is infinitely variable in its minor details. 



Astarte castanea. 



FAMILY 



GENUS Arctica 



This family is represented by one species upon the New Eng- 

 land coast, which is much sought after by collectors. It is one 

 of the larger clams, 

 but is too uncommon 

 to have received a 

 popular name and to 

 be generally well 

 known by the fisher- 

 men along the shore. 



A. (Cyprina)islan- 

 dica. This clam has a 

 thick though not pon- 

 derous shell, with promi- 

 nent beaks and a stout, 

 prominent ligament. 

 Its cardinal teeth are 

 large, but its laterals are 

 very small. A striking 

 feature of this species, 

 which at once separates 



Arctica (Cyprina) islandiea. 



