270 AXEL A. OLSSON 



from Salango, Ecuador. A more distinctive form is T. undulata (Plate 44, 

 figs. 2, 2a) which has a yellow or cream-colored shell overrun with broken, 

 lattice-like rays of brown. D'Orbigny recorded T. planulata from Coquimbo, 

 Chile, which probably refers to T. hians. 



Range — Gulf of California to northern Peru. 



Tivela (rianJtireila) hIans (Philippi) Plate 44, figures 4-4b 



Donax hians Philippi, 1851, Zeitschr. f. Mai., vol. 74 Mazatlan. 



Tivela hians (Philippi), Romer, 1864, Monogr. Molluskengatung Venus, Linne, bd. 1, 



Cytherea, 1. Sectio: Tivela, p. 9, pi. 3, fig. 3, 3a, 3b. 

 ? Tivela planulata Dall, 1909, Proc. U.S. Nat. Museum, vol. 37, No. 1704, p. 157, pi. 



28, fig. 9 {=hians, not planulata Broderip and Sovverby). 



Shell of medium size (length 55 mm.), relatively thin, subtrigonal or 

 fan-shaped, nearly equilateral, the anterior side a little longer, depressed. 

 Color usually a pale straw-yellow, marked with broken rays of purplish 

 brown, the umbones light or violet-brown. Interior flushed with grayish 

 violet, the margins white. Valves with a small gap near the posterior end. 

 Pallial sinus short. 



Length 59.7 mm., height 47.8 mm., diameter 20.8 mm. (Negritos). 



This is a common species along sandy beaches in northwestern Peru 

 south of Cabo Blanco and at many places it is gathered in large numbers 

 both for food and for fish-bait. The Peruvian shells agrees well with the 

 figures of T. hians given by Romer and were probably based on specimens 

 received from Philippi if not on the actual types. Both Philippi and Romer 

 cited Mazatlan as the type locality for this species, but I have seen no true 

 specimens north of Cabo Blanco in Peru. It is significant that Carpenter 

 did not mention the species in the Mazatlan Catalogue. Myra Keen gives 

 the range of the species as extending from Magdalena Bay, Lower California 

 to Chile. T. hians is easily distinguished from T. planulata by its thinner, 

 more depressed shell, lighter coloration, and especially by its open gap near 

 the posterior end. The anterior side is decidely longer. 



Range — Lower California to Chile. Peru: Negritos; Paita; Sechura 

 Bay; Nonura Bay to the south of Bayovar. 



Subgenus PACHTDESMA Conrad, 1845 

 Tivela (Paclij desma) argentina (Sowerby) Plate 44, figure 1 



Cytherea argentina Sowerby, 1835, Proc. Zool. Soc. London, p. 46 Nicoiyo.— Sowerby, 



1851, Thes. Conch., vol. 2, p. 622, pi. 129, fig. 62. (as Cytheraea).— Reeve, 1864, 



Conch. Icon., vol. 14, Cytherea, pi. 4, fig. 11. 

 Tivela argentina (Sowerby), Romer, 1861, Mongr. Molluskengatung Venus Linne, vol. 



1, Cytherea, 1. Secio: Tivela, pp. 17, 18, pi. 5, figs. 4, 4a, 4b.— Hertlein and 



Strong, 1948, Zoologica, vol. 33, pt. 4, No. 13, p. 166. 



Shell large, high, trigonal, with median umbones, the anterior side 

 concave or excavated by the large, elliptical, depressed lunule, the ventral 

 margin rounded. The posterior end is often slightly flexed. Color entirely 

 white, often polished with remnants of a thin, ash-gray periostracum. 



Length 57 mm., height 49 mm., diameter 16.1 mm. (a left valve from 

 Palmar, Santa Elena Peninsula). 



Generally local. Easily distinguished by its shape and white color. 



