PANAMIC-PACinc PELECYPODA 405 



Shell small (length 19 mm. or less), oblong, white, thin or of medium 

 weight, the posterior end slightly flexed. Anterior side is half again as long 

 as the posterior, slightly convex along the umbonal slope, impressed along 

 the ventral side, its end evenly rounded; the posterior side is wedge-shaped, 

 its dorsal margin somewhat flaring above, then incurved near the end which 

 is narrowly pouting or subtruncate. Surface relatively smooth but with 

 small lines of growth spaced so as to form narrow concentric ribbons, wider 

 spaced ventrally. The posterior area of the right valve is marked with 

 heavier concentric lines which are especially coarse on the zone bordering 

 the umbonal slope; small radial streaks may also be present. Pallial sinus 

 large, having its highest point in an angle just in front of the posterior 

 adductor scar, then sloping down into a rounded end, not quite extending 

 to the anterior adductor scar. Below, the sinus is confluent with the 

 pallial line. 



Length 18.7 mm., height 11 mm., semidiameter of a left valve 2.5 mm. 



This is a common and widely distributed species. It is easily recognized 

 by its shape and the heavier sculpture along its posterior surface. Fresh 

 specimens often show an iridescent luster. 



This species was cited by Hanley from Panama and from the Gulf of 

 Guayaquil, the latter place may be accepted as the general type locality. 

 It is common at Zorritos, both in beach drift and in dredgings. Hertlein 

 and Strong cite several localities north of Panama. 



Range — Gulf of California to northern Peru. Panama: San Carlos. 

 Ecuador: Santa Elena. Peru: Zorritos; Boca Pan; Talara. 



Moerella (Moerella) amianta (Dall) 



Tellina {Moerella) amianta Dall, 1900, Proc. U. S. Nat. Museum, vol. 23, No. 1210, pp. 

 303, 317, pi. 3, fig. 12. "Off Cape Tepoca near the head of the Gulf of Cali- 

 fornia." — Hertlein and Strong, 1949, Zoologica, vol. 43, pt. 2, No. 9, p. 67. — 

 Keen, 1959, Sea Shells of Tropical West America, p. 170, fig. 392. 



The shell is small, elongate, its length about twice the height, sub- 

 solid, white or glassy, the posterior side hardly flexed. The anterior side 

 is longer than the posterior, its lower and upper margins subparallel, the 

 end rounded. The posterior side is wedge-shaped, its dorsal side a little 

 flattened, smooth, its end bluntly rounded. The umbones are low, flattened, 

 the small beak projecting slightly and pointed forward. The surface is 

 sculptured with close, concentric ridges forming narrow ribbons over most 

 of the disk, but behind and on the posterior-umbonal slope they are more 

 or less fused with each other or end completely; on the posterior-dorsal area, 

 the sculpture is sharp and lamellose. There are small radial streaks as in M. 

 cerrosiana, best seen on glassy specimens. The pallial sinus is deep, almost 

 extending across to the anterior adductor scar and widely confluent with 

 the pallial line below. 



Length 12.5 mm., height 6.2 mm., diameter 3.5 mm. 



This species resembles M. cerrosiana but is larger, heavier, and longer, 

 its posterior side not so strongly flexed. 



Range — Gulf of California to Colombia. Panama: Bucaro. Colombia: 

 Isla del Gallo. 



