PANAMIC-PACIFIC PELECYPODA 181 



Adams, 1845) which was assumed to be preoccupied in birds (Gouldia 



Bonaparte, 1850). In his 1875 paper, Guppy mentioned two species as 



typical, C. pacijica and C. martinicensis. (For further discussion see 

 Gouldia.) 



Shell small, solid, subtrigonal with the lateral sides straight and gen- 

 erally subequal, the umbones flattened with the small beaks pointing 

 backwards. Anterior side rounded, the posterior generally a little longer, 

 indistinctly carinate, its end obtusely truncated or pointed. Ligament is 

 largely internal, the pit for the resilium forming a deep socket in the hinge 

 plate; it is bordered in each valve by two strong cardinal teeth on the 

 anterior side. Left valve has a strong posterior lateral tooth bordered above 

 by a linear socket. External surface smooth or with strong, concentric ribs 

 or undulations, and sometimes a microsculpture of radial lines and striae 

 best developed in the concentric troughs; this sculpture is generally not 

 visible unless the shell is fresh and unweathered. Pallial line entire, the 

 ventral margin plain. 



This is a genus of small species, usually of trigonal, flattened form with 

 small, pointed, opisthogyrate beaks, the surface smooth or with concentric 

 sculpture like that of some species of Astarte. The genus "Astarte" is cold- 

 water, its ligament external, and the ventral margin is usually strongly 

 crenulated. 



Key to Panamic Crassinella 



L Shell strongly trigonal in shape with sharply pointed beaks. Surface 

 smooth or with narrow, ridgelike concentric riblets between wide, 

 troughlike interspaces. A microsculpture often present. 



A. Concentric riblets strong and uniform over whole surface. 



1. Shell quite large for the genus (length 6 mm.), depressed, flattened. 

 Posterior margin longer than the anterior and squarely truncated at 

 the end. 



C. pacijica 



2. Shell somewhat smaller, short and high, the sides more nearly alike, 

 the posterior end not truncated. 



C. mepcicana 



3. Shell generally small, the posterior margin deeply concave, its end 

 produced into a short snout. 



C. ecuadoriana 



B. Surface smooth or nearly so. 



4. Shell small, trigonal, almost equilateral. 



C. varians 

 II. Shell less trigonal in shape, the anterior side longer. 



5. Shell small, veneriform. Surface smooth or with strong, rounded riblets. 



C. adamsi 



Crassinella paclfica (C. B. Adams) Plate 25. figures 5-5e 



Gouldia pacifica C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol. 5, pp. 499, 



545, No. 450. — Turner. 1956, Occas. Papers on Mollusks, Mus. Corap. Zool., vol. 



2, No. 20, p. 69, pi. 20, figs. 3, 4. 

 Crassinella pacifica (C. B. Adams), Pilsbry and Olsson, 1941, Proc. Acad. Nat. Sci. 



Philadelphia, vol. 93, p. 56. (fossil). — Hertlein and Strong, 1946. Zoologica, vol. 



31, pt. 3, pp. 103, 104. 



