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
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