PANAMIC-PACIFIC PELECYPODA 401 



2. Shell thinner, the anterior side high, rounded, the posterior side longer 

 than in M. meropsis, bluntly pointed at the end, the flexure obsolete. 

 Color white, yellow or pink, often with a red streak on the sides of 

 the umbone. 



M. suffusa 

 B. Shell subelliptical to subquadrate in shape, the beaks nearer the pos- 

 terior end, the anterior side hence always the longer. 



a. The posterior side narrows steadily towards the end, not indented by 

 the ligament. 



3. Shell relatively large (20 to 25 mm.), sohd and porcellaneous, white 

 in color or suffused with red. 



M. erythronotus 



b. Posterior margin arched or curved, indented by the ligament, generally 

 expanded and wider distally, its end appearing obliquely truncated. 



ba. Shell relatively large (15 mm. or more), white or red. 



4. Subquadrate, the length about half the height, the posterior end ex- 

 panded, widely truncated. 



M. arenica 



5. Broadly lenticular in shape, the anterior side much longer than the 

 posterior which is not expanded but simply rounded at the end. 



M. tumbezensis 



bb. Shell smaller. 



bba. Color usually a deep rose-red. 



6. Umbones impressed, the posterior side wide, depressed, its end truncated 

 obliquely. 



M. felix 



bbb. Color white, rarely pink. 



x. Shell small, length less than 7 mm. 



7. Posterior side cuneate. 



M. cerrosiana 

 y. Shell larger, length from 7 to 15 mm. 



8. Posterior side wide and squarely truncated at the end. 



M. recurvata 



9. Posterior-dorsal margin sinuated, terminating in a blunt, attenuated 

 point. 



10. Posterior-dorsal margin straight. 



M. hiberna 



M. amianta 

 Moerella (Moerella) meropsis (Dall) Plate 69, figures 9, 9a 



Telitna (Moerella) meropsis Dall, 1900, Proc. U. S. Nat. Museum, vol. 23, No. 1210, 



pp. 303, 317 "San Diego, Calif." 

 Tellina meropsis Dall, Grant and Gale, 1931, Mem. San Diego Soc. Nat. Hist., vol. 1, 



p. 359, pi. 14, figs. 9a, 9b; pi. 20, figs. 9a, 9b. 

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



318, pi. 3, fig. 8 "La Paz, L. Cal."— Hertlein and Strong, 1949, Zoologica, vol. 



34, pt. 2, p. 71. 



Shell small, thin or of medium texture, obliquely subovate, the anterior 

 side wide and a third longer than the posterior, full and convex along the 

 anterior umbonal slope; and in the left valve impressed behind. Posterior 

 side with its dorsal margin descending rather rapidly to form a narrowly 

 rounded or blunt point. Umbones prominent, the small beaks pointed an- 

 teriorly and projecting a little above the general profile. Surface usually 

 appearing smooth because of some wear but well-preserved specimens will 

 show a sculpture of fine, widely spaced concentric threads, best developed 

 around the anterior and ventral margins, elsewhere more or less obsolete, 



