PANAMIC-PACIFIC PELECYPODA 277 



and more widely spaced deeper lines indicating rest periods. Under the 

 lens, obscure zigzag grooves and pits are evident, best developed on the 

 posterior slope. Base color of shell is a delicate cream, penciled with a 

 pattern of fine, zigzag, brown lines and with two or more radial rays, the 

 pattern not the same on both valves. Interior white, the pallial sinus ex- 

 tends nearly to the middle, rather broad, rounded at the end. Adductor 

 scars subequal in size. 



Length 35.9 mm., height 29.1 mm., diameter 19.5 mm. (double valves). 

 Gorgona Island, off the coast of southwestern Colombia. Holotype ANSP 

 218921. 



This is probably the species recorded by Hertlein and Strong from 

 Gorgona Island as P. poUicaris; also by Dall from Panama and Peru. It 

 differs from true P. poUicaris by its smaller, thinner, and more convex 

 valves as well as stronger coloration. 



Range — Panama southward to northern Peru. Colombia: Gorgona 

 Island. Ecuador: Manta. Peru: Paita. 



Pitar (Hjpliantosoma) pollicarls (Carpenter) Plate 49, figures 7, 7a 



Diotie prora var. Reeve, 1863, Conch. Icon., vol. 14, Dione, pi. 10, fig. 45. (Not of 

 Conrad, Hawaii). Cape St. Lucas, Xantus, Lower California. 



Callista poUicaris Carpenter, 1864, Ann. and Mag. Nat. Hist., ser. 3, vol. 13, p. 312, 

 reprinted in Smith. Misc. Coll., 1872, No. 252, p. 210. New name for Dione 

 Prora var. of Reeve. — Verrill, 1870, Amer. Jour. Sci., vol. 49, p. 219. 



Pitaria poUicaris (Carpenter), Dall, 1902, Proc. U.S. Nat. Museum, vol. 26, No. 1312, 

 p. 387. 



Pitar {Hyphantosoma) poUicaris (Carpenter), Hertlein and Strong, 1948, Zoologica, 

 vol. 33, pt. 4, p. 173. 



Adult shell large {67 mm.), rather solid, subporcellaneous, widely ovate- 

 lenticular in shape, the anterior side narrowed and somewhat produced, 

 rounded at the end, the posterior side longer, widely truncated at the end. 

 The valves are only moderately inflated, externally marked with fine, con- 

 centric lines of growth and with an occasional deeper line marking a rest 

 period, surface otherwise appearing smooth, but some perfect specimens 

 may also show brown, zigzag markings, interspersed with radial rays. 



Length 65.5 mm., height 57.15 mm., diameter 36.3 mm. Carpenter's 

 type, USNM 12721. 



This is a large, thick-shelled, subporcellaneous species, smoothish but 

 with irregularly spaced, deep, concentric lines and sometimes faint divaricate 

 grooves or pits, especially on the posterior-dorsal slope which is depressed 

 or mildly excavated. The pallial sinus is deep, wide, and rounded. Lunule 

 deep, narrowly lenticular, and outlined by an incised line. 



This is a species of the Gulf of California, Records to the south, such 

 as that of Dall from Callao, Peru, are questionable, 



Pitar (Hyphantosoma) aletes Hertlein and Strong Plate 49, figure 9 



Pilar {Hyphantosoma) aletes Hertlein and Strong, 1948, Zoologica, vol. 33, pt. 4, pp. 

 172, 173, pi. 1, figs. 9, 11, 12, 13. 



Shell solid, roundly trigonal, plump, uniformly white; beaks prominent, 

 anteriorly directed over a large cordate lunule defined by a fine impressed 

 line; anterior dorsal margin short, straight, posterior dorsal margin sloping, 

 arched, with a shallow depression on each side of the hinge line and ex- 



