226 AXEL A. OLSSON 



by the right valve. When freed, the attachment area of the right valve is 

 large and flat, with spirally wound beaks of 1 ^ to 2 turns, its surface marked 

 with widely spaced concentric lines which over the hollows become 

 raised lamellae. The posterior or free side of the right valve is finely ribbed, 

 occasionally rising into small nodes. The upper or left valve it much smaller; 

 when well preserved its surface sculpture is formed mostly by small fim- 

 briated scales rising from the edges of concentrics; on the posterior side of 

 the left valve, the sculpture is formed by the edges of concentric growth 

 layers (the two-fold sculpture of Reeve). Color white, usually with small 

 hnes of brown, the area of attachment white or pink. 



Range — Lower California to Ecuador. Ecuador: Posorja; Santa Elena. 

 Panama. 



Fseuochama corrngata (Broderip) Plate 34, figures 4-4b 



Chama corrugata Broderip, 1835, Proc. Zool. Soc. London for 1834, p. 150. — Broderip, 

 1835, Trans. Zool. Soc. London, vol. 1, p. 305, pi. 38, fig. 7.— Reeve, 1846, 

 Conch. Icon., vol. 4, Chama, sp. 9, pi. 2, ifig. 9. 



Pseudochama corrugata (Broderip) Maxwell Smith, 1944, Panamic Marine Shells p. 56. 



Shell oblong-ovate to semicircular, the right valve attached as a rule 

 firmly to the substratum by the greater part of its anterior side, its umbone 

 large with prominently inrolled beak forming a deep, visceral cavity within. 

 The upper valve is much smaller and flatter, its shape depending largely 

 upon the size of the attachment area of the lower; in broadly attached 

 specimens, the shape of the shell is elongate dorso-ventrally, more circular 

 in those attached only by the anterior side of the umbone. Surface is often 

 deeply weathered and sculptureless but in good specimens, the posterior 

 side of the lower valve is finely ribbed and marked with brown lines to- 

 gether with one or more low radial ribs which may be crudely nodose. Well- 

 preserved specimens of the upper valve are sculptured with close-set, short, 

 fluted spines over the whole surface except along a narrow band on the 

 anterior side which is smooth. Color of the external surface of the upper 

 valve is generally purple. Shell cavity within may be stained a deep purple 

 or white with blotches of purple, the hinge teeth and the anterior adductor 

 scars usually purple. Inner margin of shell smooth or but obscurely 

 denticulate. 



This is the commonest of the Chamas along the north coast of Peru and 

 fossil specimens in the tablazos of Peru and Ecuador sometimes reach a 

 much larger size than any Recent examples seen. The species is easily 

 recognized by its deep purple color of its interior, or the cavity of the 

 shell within may be white or yellow but the anterior adductor scar and 

 the hinge teeth remain stained with purple. It is usually attached by the 

 entire anterior surface of its right valve, the resulting form is, therefore, 

 an elongate ovate shell lengthened along the dorso-ventral axis. 



Range — Panama southward to northern Peru. Peru: Sechura Bay; 

 Paita, Negritos; Lobitos; Mancora, Caleta Sal; Zorritos. Ecuador: Santa 

 Elena, Mancora, Mompiche. Panama: Puerto Mensabi; Bucaro; Montijo 

 Bay. 



