PANAMIC-PACIFIC PELECYPODA «7 



}Coelodon radians Dall, 1915, Proc. U.S. Nat. Museum, vol. 49, No. 2116, pp. 450, 451 

 Ballenas Lagoon, Lower California, in 5J/2 fathoms. 



Shell relatively small, delicate, half-round, arcuate behind the beaks, 

 compressed with the anterior area defined by an impressed line but not in- 

 terrupting the basal margin. Posterior side a little attenuated with a rib 

 near the dorsal margin. Valves unequal, the left one convex, the right valve 

 flat, and marked with radiating linear grooves. 



Length 15 mm., height 8.75 mm., diameter 3.75 mm. (Sowerby's 

 measurements of radiata). 



Length 15 mm., height 8 mm., diameter 1.3 mm., beaks behind the an- 

 terior end, 3.5 mm. (Dall's measurements for radians). 



The type specimen of this species was described from Isla del Muerto in 

 the Gulf of Guayaquil. The shell described by Dall as Coelodon radians from 

 the Gulf of California may be the same species. 



Range — Gulf of California southward to Ecuador. Mexico: Ballenas 

 lagoon. Ecuador: Isla del Muerto. 



Subgenus FOVEADENS Dall, 1915 

 Type species by original designation, Foveadens panamensis Dall. 

 Panama. 



Shell pandoriform, the valves almost alike, flattened or depressed, the 

 left one slightly the larger. The hinge of the right valve has two, large, 

 divergent, crural laminae under the beak, the arms of which form a V, the 

 first lamina under the beak is short, narrow and vertical, the other is much 

 longer, narrow, bent towards the end; there is only a faint indication of an 

 anterior ridge extending to the adductor scar. The left valve has two, short, 

 anterior teeth or laminae placed close together, their ends turned sharply 

 forward; there is a third, much longer, posterior, crural lamina bordered 

 on its inner side, first by the insertion groove for the lamina of the opposite 

 valve, and below this by the larger scar of the resilum. Behind the left, 

 posterior lamina, there is a deep groove or furrow which is extended for- 

 ward and passes under a decklike sheet fused with the dorsal margin. 



Pandora (Foreadens) panamensis Dall Plate 81, figures 2-2b 



Foveadens panamensis Dall, 1915, Proc. U.S. Nat. Museum, vol. 49, No. 2116, p. 451 



"Old Panama." 

 Pandora {Foveadens) panamensis Dall, Hertlein and Strong, 1946, Zoologica, vol. 31, 



pt. 3, No. 8, p. 98. 



Full-grown specimens attain a length of 25 to 26 mm., but are usually 

 smaller; both valves are nearly flat, the right valve a trifle larger, over- 

 lapping the other by a flattened edge along the posterior-dorsal margin. 

 Near the anterior one-third, the disk is divided into two unequal areas by 

 a Hne running from the beak to the ventral margin. Surface smooth or with 

 coarse, concentric growth lines and sometimes faintly undulate. Outer layer 

 thin, white, chalky, often worn-off revealing the heavier, pearly layer 

 beneath. 



Old Panama, abundant. 



Range — El Salvador to Panama. Panama: Old Panama; Pearl Islands. 



Family THRACIIDAE 

 Shell non-nacreous, thin or of medium weight, oblong, sometimes 



