PANAMIC-PACIFIC PELECYPODA S4J 



down into a more narrowly rounded end. Surface smooth but with a neat 

 sculpture of minute radial threads, their interspaces lined and finely pitted, 

 especially over the umbones, merging into waved concentrics on the pos- 

 terior slope. Length 11 mm., height 8.8 mm., diameter 1.1 mm. (Bucaro, 

 Panama). 



A small but easily recognizable species, apparently rare at all localities. 

 Some records of D. ohesus in the literature may be based on young speci- 

 mens of some other species. The type of this interesting species is in the 

 D'Orbigny collection at the British Museum (Natural History). 



Range — Panama southward to Peru. Panama: Bucaro. Peru: Paita. 



Subgenus BIACHAERODON AX Romer. 1870 

 Type species by subsequent designation, Dall, 1900, Donax scalpellum, 

 Gray. 



Shell elongated, razor-shaped, relatively thin, the posterior side short, 

 its umbonal carination sharp and bordering a deeply impressed and more 

 strongly sculptured posterior area, the rest of the surface smooth. Margins 

 crenulated. Valves are open with a gap at both ends. 



Donax (Machaerodonax) transversus Sowerby Plate 59, figures 4-4b 



Donax transversa Sowerby, 1825, Cat. Shells Tankerville, Ap. p. IV.— Reeve, 1954, 



Conch. Icon., vol. 8, Donax, pi. 6, fig. 36. 

 Donax transversus Sowerby, Sowerby, 1866, Thes. Conch., vol. 3, Donax, p. 306, No. 



6, pi. 280, fig. 11. — Hertlein and Strong, 1949, Zoologica, vol. 34, pt. 4, p. 256, pi. 



1, fig. 3. 



Shell with elongate, soleniform, and moderately convex valves, the 

 anterior side the longer, the dorsal and ventral margins more or less parallel 

 except at the anterior end where the dorsal margin is slightly concave. The 

 valves have an open gap at both ends. The posterior side is short, set off 

 by a sharp, umbonal keel, the posterior slope depressed or flattened and 

 with an angle or keel in the middle forming an open gap at the margin. Sur- 

 face glossy, mainly smooth but with fine, radial lineation showing through; 

 on the posterior slope, the sculpture is stronger, formed by finely beaded 

 and cancellated riblets. The usual color of the surface is white rayed with 

 broad belts of violet and purple, generally lightly tinted with yellow produced 

 mainly by the thin layer of periostracum. Interior of valves purple. The 

 largest shells may attain a length of about 40 mm. 



Length 37.2 mm., height 14.7 mm., diameter 10.2 mm. Manglaralto, 

 Ecuador. 



Range — Mexico to northern Peru. Mexico: Mazatlan. Nicaragua: 

 Corintho. Panama: Bucaro; Guanico; Burica Peninsula. Ecuador: Mon- 

 tanita, near Manglaralto; San Lorenzo; Punta Blanca; Santa Elena; Ancon 

 Point. Peru: Punta Picos; Caleto Sal; Mancora; Paita. 



Subgenus AMPHICHAENA P"hilippi, 1847 



Type species by monotypy, A. kindermanni Philippi (= Z). culter 

 Hanley, 1845). 



Shell elongated, often irregular tageloid, the beaks are placed a little 

 behind the middle, the posterior side, therefore, the longer, expanded, the 

 valves thin, the margins crenulated. 



