PANAMIC-PACIFIC PELECYPODA 285 



Shell ovate, the posterior side longer, the end bluntly rounded. The 

 concentric lamellae are of medium-strength, flatly reflexed, wider than their 

 interspaces, each eighth or tenth lamellae on the anterior slope, larger and 

 more lamellose; they terminate sharply at the posterior-umbonal angle 

 and there each third or fourth is raised to form a short spine. Color white, 

 more often brown or chestnut-red, the lunule and the posterior-dorsal slope 

 more deeply marked. 



Length 47.9 mm., height 39.4 mm., diameter 10.5 mm. (right valve 

 from Manglaralto, near Santa Elena. 



Range — Gulf of California to northern Peru. Panama: Burica Penin- 

 sula; Gulf of Chiriqui; Guanico; Bucaro. Colombia: Isla del Gallo. Ecuador: 

 Mompiche; San Francisco; Manglaralto; Santa Elena. Peru: Tumbez. 



Genus LAMELLICONCHA Dall, 1902 



Type species by original designation, Cytherea concinna Sowerby. 



Shell trigonal or ovate, convex or subcompressed, thin or subsolid, 

 sculptured concentrically with low, raised ridges or solid, rounded laminae 

 which begin at the edge of the lunule and extend across the disk to the 

 posterior-dorsal margin. Lunule cordate, deeply impressed, smooth; no 

 escutcheon. The hinge is like that of Pilar or Hysteroconcha with a large, 

 sharp, anterior lateral tooth in the left valve and its socket in the right. 

 Pallial sinus large and deep. Color white or rose-brown, often with radial 

 rays. 



Key to species of Lamelliconcha 



L Sculpture produced by low, rounded, rather solid and closely spaced 

 concentric riblets. 



A. Shell subovate to elongate in shape, the posterior side somewhat lower 

 and produced, the posterior-ventral margin often indented ar weakly 

 sinuated. Umbones low and inconspicuous. 



a. Posterior-dorsal submargin flattened and angled. Shell strongly colored. 

 \. Subovate to trigonal in shape, convex, the concentrics numerous. 



L. concinna 



2. Usually longer and more compressed, the concentrics stronger. 



L. -paytensis 



b. Posterior-dorsal submargins rounded. 



3. Color usually white. 



L. tortuosa 



B. Shell subovate, cordate, solid. Concentrics usually evanescent over the 

 middle of the shell disk. 



4. Color a uniform white or brown. 



L. unicolor 

 IL Surface sculpture more strongly lamellose, the concentrics forming 

 thin, elevated, sharp-edged laminae. Shell generally rounded, cordate, 

 with high, prominent umbones. 



C. Concentrics numerous and closely spaced, uniform in strength or 

 slightly alternate. 



Group of L. circinata 



5. Shell large (length 40 mm. or more), usually white or with the umbones 

 rayed with violet. The lunule and escutcheon are colored chestnut- 

 brown. 



L. circinata alternata 



