PANAMIC-PACIFIC PELECYPODA 297 



Shell small (length seldom above 25 mm.), elongately ovate, rather 

 solid, with a wide, elliptical escutcheon, flattened and nearly as long as the 

 dorsal side; the lunule large, cordate, and flat. The sculpture is produced 

 by high, strong, concentric riblets, solid in structure, between wide, flat 

 interspaces, the crests of the riblets rounded or narrowly reflexed doTsally 

 except at the posterior end where they are sharply narrowed and raised, 

 sometimes with an obscure tooth at their ends. Both riblets and interspaces 

 are smooth except for concentric growth lines, radial striae are faint or 

 missing. General color is a cream white, often with three or more brown rays 

 extending across from the beaks; the lunule and escutcheon is usually 

 brown. 



Length 22.8 mm., height 17.1 mm., diameter 12.4 mm. Punta Blanca, 

 Ecuador. 



This is a common and widespread species often appearing on some 

 beaches in great numbers, usually as loose valves. The shell is somewhat 

 variable in shape and in the size and spacing of the concentric riblets. 

 Shells from Ecuador are usually larger than those from Panama and often 

 show the strongly produced posterior end as illustrated by the original 

 types from Isla la Plata. 



Range — Lower California to northern Peru. Panama: Rey Island, 

 Pearl Islands; Bucaro; Guanico; San Carlos. Panama Canal Zone: Amador 

 Beach; Venado Beach. Colombia: Isla del Gallo. Ecuador: Mompiche; 

 Charapota; Manta; Punta Blanca; Santa Elena. Peru: Zorritos; Mancora; 

 Lobitos. 



Subgenus ILIOCHIONE, new subgenus 

 Type species, Venus subrugosa Sowerby, 1853 (:=Venus subrugosa 

 Wood). 



Shell ovate to elongate subtrigonal, solid. Sculpture produced by 

 coarse, rounded concentric folds, strong and regular on the umbones, lower 

 and irregular below the middle of the disk and often obsolete or nearly so 

 near the ventral margin. The concentrics and their intervals are overrun 

 by fine, regular, radial incised lines forming small flat riblets, but these also 

 fade out ventrally. The posterior-umbonal angle is enlarged to form a strong, 

 cordlike fold along the side of the umbone, weaker distally. Color varied 

 and often with an elaborate pattern of rays and small spots of brown on a 

 white base. Hinge and pallial sinus of Chione, s.s. Mostly on mud flats and 

 similar habitat stations. 



Species of this subgenus have usually been referred to Anomalocardia 

 Schumacher (type species, Venus rugosa Schumacher=F. jlexuosa Linne), 

 but they are more closely allied to Chione. The genus Anomalocardia is a 

 West Indian and Caribbean group, as yet unknown in the Pacific region. 



Two Recent species distinguished as follows: 



I. The posterior-umbonal rib is strong. Concentric riblets numerous and 

 cover a major part of the shell disk, absent only from close to the 

 ventral margin. Peru northward. 



C. subrugosa 



