PANAMIC-PACIFIC PELECYPODA S29 



ternally by coarse lines of growth and covered by a thin, yellowish perio- 

 stracum. 



Length 130 mm., height 94 mm., semidiameter 30 mm. a left valve, 

 Guanico, Panama. 



Known also as fossil in the Miocene of Peru and Costa Rica. 



Range — Gulf of California to northern Peru. Panama: Burica; Bucaro; 

 Guanico; San Carlos. Colombia: Choco; Isla del Gallo. Ecuador: Santa 

 Elena. Peru: Tumbez; Punta Picos; Caleto Sal. 



Genus HARYELLA Gray, 1853 

 Type species by monotypy, Harvella elegans (Sowerby). 



Shell rounded, convex, concentrically plicate, extremely thin. Pos- 

 terior-dorsal area narrow but well defined by an outer ridge against which 

 the concentric plicae end sharply. Lunule broadly cordate, deeply im- 

 pressed, smooth. Hinge, with the general pattern of Mactrellonn, has a large 

 chondrophore in the middle bordered on the anterior side by an inverted, 

 V-shaped, cardinal tooth. The sockets for the lateral teeth in the left valve 

 are deep, the anterior one with a small accessory lamina on the dorsal wall. 

 External ligament is small. 



Key to Panamic-Pacific species 



I. Surface undulations are strong and deep, with nearly circular curve, 

 concentric to the margin and spaced evenly over the whole disk. 



1. Concentric plications are widely spaced (about 4 mm. apart). Height 

 of shell usually less than 60 mm. 



H. elegans 



2. Shell larger and heavier, the concentric undulations smaller and more 

 numerous (spaced about 3 mm. apart). 



H. elegans tucilla 

 II. Concentric undulations have a sharp, V-shaped bend in the middle. 



H. goniocyma 



Harvella elegans (Sowerby) Plate 56, figures 5-5b 



Mactra elegans Sowerby, 1825, Cat. Shells Tankerville, p. 11, pi. 1, fig. 3. — Reeve, 



1854, Conch. Icon., vol. 8, Mactra, pi. 17, fig. 89. 

 Harvella elegans (Sowerby), H. and A. Adams, 1856, Genera Recent Shells, vol. 2, 



p. 378, pi. 99, figs. 4, 4a. 

 Harvella pacifica Conrad, 1867, Amer. Jour. Conch., vol. 3, pt. 2, p. 192. — Conrad, 



1869, op. cit., vol. 5, pt. 2, p. 108, pi. 12, fig. 2. 

 Mactrella {Harvella) elegans (Sowerby), Hertlein and Strong, 1950, Zoologica, vol. 



35, pt. 4, p. 235. 



Shell thin, white, roundly trigonal, the ventral margin forming the 

 half circumference of a circle, the umbonal portion subtrigonal, convex. 

 Sculpture is formed by strong, narrow, concentric ribs between deep, wide 

 interspaces which run across the disk from a deeply sunken, smooth lunule 

 to the edge of a posterior keel. Posterior-dorsal area smooth. Substance of 

 shell thin, the concentric ribs showing through on the inside in the reverse 

 or as concentric grooves. 



Length 60.5 mm., height SL3 mm., diameter 38.5 mm. 



Although poorly represented in most museum collections, the loose 

 valves of this fine mactrid is not uncommon along open beaches from Peru 

 northward. It is now strictly a Pacific species but in Miocene times, there 

 were several allied forms in the Caribbean region. H. elegans tucilla Olsson 



