274 AXEL A. OLSSON 



Range — Lower California to northern Peru. Lobos Islands. Panama: 

 Pearl Islands; Burica Peninsula. Ecuador: Manta; Isla la Plata; San Pedro, 

 near Manglaralto; Santa Elena. Peru: Mancora; Lobos de Tierra. 



Genus PITAB Romer, 1857 

 (Caryatis Romer, 1862; Pitaria Dall, 1902, emendation.) 



Type species by monotypy, Cytherea tumens Gmelin. 



Shell subtrigonal or subovate, inequilateral with convex umbones and 

 small adjacent beaks. Lunule cordate or elliptical, defined by a faintly 

 incised line, no escutcheon. Surface sculptured principally with fine hairlike 

 concentric or growth incremental, sometimes with superimposed zigzag 

 grooves. Hinge with a strong, anterior lateral tooth in the left valve and 

 its socket in the right. Cardinal teeth three in each valve; the left valve has 

 the central and anterior cardinal teeth joined above forming an inverted 

 V, the enclosed pit below forming the socket for the central cardinal tooth 

 of the opposite valve; right valve has the anterior and posterior cardinal 

 teeth joined forming a single lamellar structure which in a rooflike fashion 

 overhangs the smaller, free-standing, central cardinal tooth below. Pallial 

 sinus is large and extends nearly to the middle of the valve cavity. Inner 

 ventral margins smooth. 



May be divided into two subgenera as follows: 



I. Surface plainly sculptured with growth incrementals only. 



Subgenus Pitar, s.s. 



II. Like Pitar but in addition has a superimposed system of zigzag grooves 



and punctae, usually best developed along the ventral slope (in some 

 species of inconstant development). 



Subgenus Hyphantosoma 



Pitar (Pitar) consangnlnens (C. B. Adams) Plate 45, figures 3-3a 



Cytherea consanguinea C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol. 5, 

 pp. 496, S4S, No. 445 Panama. — Romer, 1867, Mongr. Molluskengatung Venus 

 Linne, bd. 1, Cytherea, p. 108, pi. 28, figs. 5, 5a, 5b.— Sowerby, 1853, Thes. 

 Conch., vol. 2, p. 743, pi. 163, fig. 203. — Turner, 1956, Occas. Papers on Mollusks, 

 Mus. Comp. Zool., vol. 2, No. 20, pp. 42, 43. Types lost. 



Pitar {Pitar) consanguineus (C. B. Adams), Hertlein and Strong, 1948, Zoologica, vol. 

 3, pt. 4, No. 13, pp. 170, 171.— Hertlein and Strong, 1955, Bull. Amer. Mus. 

 Nat. Hist., vol. 107, No. 2, p. 189. 



The shell is relatively small, (average length from 30 to 33 mm.), 

 rounded trigonal to subovate, moderately convex, the umbones prominent 

 and full, placed near the anterior one-third, the beaks curved over a 

 relatively large, cordate lunule outlined by a faint line and deeply impressed 

 in the middle. Viewed from the inside, the two ends of the valve appear 

 almost equally rounded but the anterior one is more narrow and its 

 dorsal-lunular margin is straight. The surface is covered with rather strong, 

 concentrics, especially so on the anterior slope. The primary color of the 

 shell is a cream-white, plain or with brownish, radial rays on the umbones 

 and sometimes broken arrow-shaped or zigzagged lines. The inner portion 

 of the lunular surface is usually colored a deep brown, also some part of 

 the posterior-dorsal surface. The pallial sinus is well developed and extends 

 nearly to the middle of the cavity of the valve. 



