NO. 2 ROST: THE FAMILY ARCIDAE 203 



Hancock collections. The larger one, from Isla Isabel, Mexico, meas- 

 ures 54.5 mm in length, 31.7 mm in height, and 27.4 mm in diameter. 

 It fits Reeve's description very closely and must represent this species, 

 despite its much larger size and more northerly locality. The other 

 specimen, from Islas Secas, Panama, measures 34.6 mm in length, 21.2 

 mm in height, and 18.3 mm in diameter, and agrees completely with the 

 larger example. One specimen in the San Diego Museum of Natural 

 History (cat. no. 28182) is labelled "Carmen Island, Gulf of Cali- 

 fornia, 20 fms." Its length is 27 mm and it agrees completely with the 

 specimens at hand. The shells possess 37 to 39 ribs. The periostracum is 

 dark brown and bristly in the interspaces between the ribs. Posteriorly 

 the bristles become very long but are still soft. On the ribs the perio- 

 stracum forms membranous lamellae which are of a lighter color. The 

 ligament has two chevron-shaped grooves. Between one third and one 

 fourth of the ligament is situated anterior to the umbones. A black ray 

 on the umbones as described by Maury (1922) cannot be observed. 

 This species was designated by Stewart (1930) as the type of the sub- 

 genus Cara Gray. 



Occurrence: Rare. Taken between 10 and 20 fms, on various kinds of 

 bottom, sand, mud, rock, coralline, etc. 



Distribution: Isla del Carmen, west coast of the Gulf of California 

 (San Diego Museum), to Santa Elena, Ecuador. 



Anadara (Scapharca) emarginata (Sowerby) 1833 



PI. 14, fig. 22; text-figs. 89 a-c 



Area emarginata Sowerby, Proc. Zool. Soc. London, 1833, p. 20. 

 Fig.: Reeve, 1844, PL 4, fig. 26; Maury, 1922, PI. 2, figs. 5, 10. 

 Type loc: Atacames, Ecuador (designated by Hertlein and Strong, 



1943). 

 Holotype: British Museum? 



Remarks: The material at hand contains only small specimens less than 

 18 mm in length. The umbones are decorated with a blue, bluish-green, 

 or black radiating ray, and the rest of the shell has black blotches. Some- 

 times black lines radiating from the umbo are present in the interior of 

 the shell (cfr. Carpenter, 1856a, p. 137). The ribs are about 30 in 

 number. The five or six most anterior and three or four most posterior 

 ribs are often crossed by transverse ridges. The posterior auriculation 

 is variably pronounced. The byssus is well developed and intact in some 

 of the specimens. The mantle margin is pigmented with a dark brown 



