PANAMIC-PACIFIC PELECYPODA 431 



contracted and flattened thus adding to the convexity of the shell. Adults 

 have a strongly produced, snoutlike, posterior end, that of the left valve 

 formed by discrete, accessory lamellae. The sculpture is formed by con- 

 centric riblets, strongest near the ventral margin, and in addition, the sur- 

 face is covered with fine or coarse, radial lines which sometimes form deep 

 grooves, the space between them forming flattened rays of irregular width 

 and on higher magnification reveal a series of minute pimples or granules, 

 (Usually set in pairs. This radial sculpture is best brought out if the speci- 

 mens are slightly weathered. 



As noted by Hertlein and Strong, the identification of Corbula ohesa of 

 Hinds is uncertain, its small-sized figure and incomplete description is not 

 sufficient for an exact identification. (See also under C. porcella). 



Range — Lower California to northern Peru. Mexico: Concepcion Bay and 

 Tangola-Tangola Bay (both Hertlein and Strong). Nicaragua: Real Llejos 

 (Cuming). Costa Rica: Gulf of Nicoya (Hertlein and Strong). Panama: 

 Bucaro. Ecuador: Guayaquil (Cuming); Puerto Limones. Peru: Zorritos. 



Caryocorbula (Caryoeorbula) porcella (Dall) Plate 76, figure 8 



Corbula porcella Dall, 1916, Proc. U.S. Nat. Museum, vol. 52, No. 2183, pp. 415, 416 

 off Lower California in 44 fathoms, mud.— Dall, 1921, Bull. 112, U. S. Nat. 

 Museum, p. 54. Range Santa Rosa, Calif., to Panama. 



Aloidis {Caryocorbula) porcella (Dall), Hertlein and Strong, 1950, Zoologica, vol. 35, 

 pt. 4, p. 242, pi. 2, figs. 13, 15. 



Shell small, whitish, short-rhombic, the umbones wide, low, submedian, 

 the anterior side rounded, the posterior side a little longer, obliquely trun- 

 cated at the end, slightly curved or pouting at the lower extremity. The 

 valves are nearly alike in convexity and shape, left being a trifle smaller 

 and overlapped widely by the right valve along the posterior-ventral margin. 

 Surface with the umbones usually smooth but with heavier or coarser, 

 rounded, concentric riblets showing near the ventral margin. The rostrum 

 is short but defined by an angled edge, its surface often with strong cross 

 sculpture or if smoother, its surface is often minutely granulose, especially 

 iSo in the case of the right valve. Color usually a dirty white, with clay 

 -particles adherent, and covered by a thin olive periostracum, the interior 

 white. The species varies somewhat in size and general dimensions. Dall's 

 type measures: length 8.5 mm., height 4 mm., diameter 4.5 mm. 



The above description is based on typical specimens of S. porcella in 

 the U. S. National Museum. As pointed out by Hertlein and Strong, this 

 species is perhaps C. obesa Hinds (see under C. nuciformis). Hinds made 

 no mention of radial striations but this minute sculpture could easily have 

 been overlooked. On most specimens of C. porcella examined, the concentric 

 riblets are smooth over the surface of the disk, the minute granules or 

 shagreenation developed only on the rostral surface. The range of C. porcella 

 as given by Dall, is from Lower California to Panama, but records south 

 of Mexico require confirmation. 



Caryocorbula (Caryocorbula) marmorata (Hinds) Plate 75. figure 5 



Corbula marmorata Hinds, 1843, Proc. Zool. Soc. London, p. 58 west coast of Veragua 

 from 26 fathoms, mud. — Hinds, 1845, Zool. Voy. Sulphur, Moll. pt. 3, p. 69, pi. 

 20, fig. 13.— Reeve, 1844, Conch. Icon., vol. 2, Corbula, pi. 5, fig. 39. 



