268 AXEL A. OLSSON 



pointed at the end. Color white or in varying shades of brown or chestnut, 

 sometimes quite dark, strongly rayed or with broken, lattice-like markings. 

 Tip of beaks purple. 



Length 36.7 mm., height 31.5 mm., diameter 23 mm. Mompiche, 

 Ecuador. 



This species is similar to T. mactroides Born of the Caribbean and 

 some specimens cannot be effectively separated if their derivation or locality 

 station is unknown. The types of T. radiata are preserved at the British 

 Museum (Nat. Hist.); they are somewhat larger than the average, the 

 largest specimen measures about 62.5 mm. in length. These specimens of 

 T. radiata are similar to shells of T. mactroides from the Caribbean coasts 

 of Colombia and Venezuela. Good figures of T. radiata are given by Romer. 

 T. bryonensis sports several color variations, some of which have been 

 named; the common form found along the coast of northern Peru and the 

 Gulf of Guayaquil is usually a pale chestnut yellow with the umbones 

 marked with lattice-like brown lines; this form was named "hindsii" by 

 Hanley: similar pale-colored shells were designated semifulva by Menke, 

 and as gracilior by Sowerby, figures of which are given in Romer. T. puUa 

 is a small, rayed form of the above. In most specimens of T. bryonensis, 

 the beaks and part of the umbones is stained with purple, a character 

 also shared with T. mactroides. 



Range — Lower California to northern Peru. Panama: Old Panama; 

 Bucaro; Guanico; San Carlos; Pearl Islands. Ecuador: Mompiche; Sua; 

 Manglaralto; Manta; Punta Blanca; Santa Elena. Peru: Tumbez; Boca 

 Pan; Mancora; Organos. 



Tivela (Tivela) delessertil (DeshayeiS in Sowerby) Plate 44, figures 9, 9a 



Cytheraea nitidula Lamarck, Sowerby, 1851, Thes. Concli., vol. 2, p. 616, No. 14, pi. 

 128, fig. 25. Not C. nitidula Lamarck. 



Cytheraea delessertii Deshayes in Sowerby, 1854, Thes. Conch., vol. 2, p. 785. Re- 

 naming of C. nitidula, p. 616, pi. 28, fig. 25. 



Tivela arguta Romer, 1861, Malak. Blatter., vol. 7, p. 148. — Romer, 1862, Dunker Novit. 

 Conch. Lief., vol. 4, No. 39, No. 37, t. 12, figs. 7, 8, 9.— Romer, 1865, Mongr. 

 Molluskengattung Venus, Linne, bd. 1, Cytherea, 1. Sectio: Tivela, pp. 15, 16, 

 pi. 4, figs. 5, 5a, 5b Panama. 



Tivela delessertii (Deshayes in Sowerby), Hertlein and Strong, 1948, Zoologica, vol. 

 33, pt. 4, No. 13, p. 167, pi. 2, fig. 10. 



Shell usually small (average length about 30 mm.), elongately trigonal 

 or I'phigena-X^^ in shape, noticeably longer than high, the posterior side 

 longer and attenuated at the end, the anterior end more rounded. Coloration 

 varied, sometimes pure white, more often the surface is clouded with brown, 

 often with rays and zigzag lines. The umbonal cavity is usually a deep, 

 violet-brown, the marginal area white. 



Length 29.2 mm., height 23 mm., diameter 16.4 mm. Acapulco, Mexico. 



Length 40.2 mm., height 31.3 mm., diameter 18.6 mm. Pearl Islands, 

 Panama. 



This species is common at Acapulco, rare at most other localities. 

 Range — Lower California to Panama. Mexico: Acapulco. Panama: 

 Gibraleon and Bayoneta Islands, Pearl Islands. 



