PANAMIC-PACIFIC PELECYPODA 315 



one-third. The anterior side is short, attentuated, the fullness of the valve 

 is usually greatest along the umbonal slope to a point just behind the 

 middle of the ventral margin. The sculpture is produced by narrow, raised 

 concentric riblets, their sides and intervals decussated by radials. Color 

 white or cream, the interior blotched with deep, mahogany-brown, deepest 

 on the ends and along the margins. Posterior end gaping. 



Length 33.8 mm., height 20.7 mm., diameter 20 mm. 



Length 32 mm., height 14.2 mm., diameter 14.4 mm. 



Santa Elena, Ecuador, 



This is a common species along the coast of northern Peru and Ecuador; 

 its shape variable depending upon the hardness or softness of the medium 

 in which it bored. The typical form is elongated; the anterior end short, 

 constricted, and attenuated. 



Range — Gulf of California to Peru. Panama: Bucaro; Puerto Mensabi. 

 Ecuador: Sua; Galeras; Crucitas; Manta; Santa Elena. Peru: Paita; 

 Bayovar. 



Petricola (Petricola) peruviana, new species Plate 55, figure 9 



Shell irregularly subrectangular, with the umbone and beak placed 

 near the anterior one-th!rd, the anterior side hence short, rounded at the 

 end, the posterior side much longer, its dorsal and ventral margins sub- 

 parallel, the posterior end widely rounded and gaping. Surface sculpture 

 is formed by rather fine radial riblets, more or less uniform over the whole 

 disk. Concentrics are limited to lines of growth and irregular undulations. 

 Pallial sinus large, rounded, and extending nearly to the middle of the shell 

 cavity. Color white or cream, the posterior end stained with brown. 



Length 30 mm., height 21 mm., semidiameter 7.3 mm. a left valve, 

 Paratype, ANSP 218906. 



Length 30 mm., height 19.1 mm., semidiameter 5.4 mm. a right valve, 

 Holotype, ANSP 218905. 



Range — Ecuador to northern Peru. Ecuador: Santa Elena. Peru: 

 Tumbez; Mancora; Lobitos; Negritos; Paita; Bayovar. 



Petricola (Petricola) robusta Sowerby Plate 54, figures 2, 2a 



Petricola robusta Sowerby, 1834, Proc. Zool. Soc. London, p. 47. — Sowerby, 1854, Thes. 

 Conch., vol. 2, Petricola, pi. 166, figs. 16, 17. — Sowerby, 1874, Conch. Icon., 

 vol. 19, Petricola, pi. 3, fig. 20a, 20b Panama and Isla Muerte. 



Petricola {Petricola) robusta Sowerby, Hertlein and Strong, 1948, Zoologica, vol. 33, 

 pt. 4, No. 13, p. 194. 



Shell ovate-trigonal, the anterior side convex with rounded margin, 

 the posterior side narrowed and produced. Sculpture is formed by simple 

 radial riblets, coarse on the posterior side much finer on the anterior, waved 

 and slightly broken by concentric lines marking intervals of growth. 



Length 24.3 mm., height 19.1 mm., diameter 16.1 mm. From the shell 

 of a large Spondylus. Punta Montanita, Ecuador. 



Range — Gulf of California to northern Peru. Ecuador: Santa Elena; 

 Punta IVIontanita. Peru: Boca Pan; Caleta Sal. 



Subgenus PETRICOLARIA Stoliczk:i, 1870 



Type species by original designation, P. pholadiformis Lamarck. Recent, 

 Maritime Provinces of Canada, southward to the West Indies. 



