SYNOPSIS OF THP: family ASTARTIDyE, WITH A KE\'1KW 

 OF THE AMERICAN SPECIES. 



By William Healey Dall, 



Honorary Cvrntnr, Dirmon of MoUusks. 



The group of bivalve shells which composes this family is of ancient 

 origin, the Crassatellitida' having diverged from it in the later Mcso- 

 zoic and taken definite form in the Eocene. The chief characteristic 

 by which the two families are discriminated is found in the ligament, 

 which in Astartidx is external as well as the resilium, whiU' in the 

 Grassatellitidae, this organ is separated from the resilium, the lattei-. 

 except in ErlpKyla, being deeply immersed. In Er/jdn/Ja the process 

 has only begun, but the other characteristics of the shell are so close 

 to Crassinella that the two must obviously be associated in the same 

 family. In Lirodlscns of the A.stdiitdx the resilium is separateil from 

 the ligament, but still remains external, while the other characters link 

 it to Astarte in a way analogous to those which bind Er'iplnjJn to the 

 Crassinellas; so each family has an exceptional and peripheral group. 



Concentric sculpture, dense periostracum, absence of bright color 



pattern, and a hinge formula of, in its fullest development, the fol- 



, . - ^ /LO. 101010. 1\ , , . ^. . „ • . -I 



lowmg elements I pi 01 01 01 n / '^^"^ characteristic of this family, as is 



its preference for cold waters, the tropical species keeping chielly in 

 the cold abysses or l)eing dwarfed in size. The CramddHtid», on the 

 other hand, are prevalent in the Tropics and unknown in the cold sea.s. 

 I have not found more than three cardinals in either valve, and there 

 are usually several nearly obsolete. The laterals are formed by an 

 extension of the valve margin, which fits into a groove or socket in 

 the opposite valve. These are usually alternated, one lateral and one 

 socket to each valve. The middle cardinals are usually well developed 

 and sometimes bifid, the anterior right and posterior left cardinals 

 always (and the posterior right cardinal often) more or less obsolete. 

 The sides of the cardinal teeth are frequently vertically striated, as in 

 CrasmteUites^ especially in the fossil species. 



Proceedings U. S. National Museum, Vol. XXVI— No. 1342. 



933 



