182 AXEL A. OLSSON 



Shell subtriangular, depressed or flattened, with the beaks nearly 

 median, trigonal and pointed, usually inclined a little backwards, the ven- 

 tral margin widely rounded. The two marginal sides are nearly alike, the 

 posterior a little longer, straight or a little concave, becoming typically 

 somewhat truncated at its end. Surface is covered uniformly with large, 

 widely spaced, concentric ridges between wavelike troughs, usually between 

 8 to 12 in number. In addition, there is a fine, microscopic radial striation, 

 heaviest in the concentric troughs, to be seen on fresh specimens. Color 

 is variable, ranging from pure white to various shades of brown, purple 

 and pink, often with narrow lines of brown radiating from the beaks. 



Length 6.1 mm., height 5.7 mm., diameter 2.6 mm. Panama City. 



This is the largest and commonest species of Crassinella in the Panamic 

 fauna and is distinguished from the somewhat similar C. mexicana Pilsbry 

 and Lowe (which is nearly equilateral) by its somewhat longer posterior 

 side which at the end is wider as if sharply truncated. The concentric un- 

 dulations are strong, rising as narrow ridges between wide, wavelike troughs. 

 Fresh specimens show a fine pattern of submicroscopic, radial striations 

 which may appear as divisions between rows of parallel oblong dots (Car- 

 penter's strung-fig pattern) but this structure is quickly destroyed by 

 beach wear. C. pacifica is closely related and perhaps conspecific with C. 

 mactracea Linsley of the Atlantic and the Miocene C. lunulata Conrad. 



Range — Gulf of Panama southward to Peru. Panama: Bucaro; Panama 

 City; Las Tablas. Colombia: Isla del Gallo. Ecuador: Manta; Punta Blanca; 

 Puerto Callo. Peru: Zorritos. 



Crassinella mexicana Pilsbry and Lowe Plate 25, figure 4 



Crassinella mexicana Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 



84, pp. 103, 104, pi. 14, figs. 8, 9 Guaymas, Mexico. 

 Crassinella pacifica mexicana Pilsbry and Lowe, Hertlein and Strong, 1946, Zoologica, 



vol. 31, pt. 3, p. 104. 



The shell is similar to C. pacifica (C. B. Ad.), from which it differs 

 chiefly by being relatively high and short, the posterior and anterior dorsal 

 margins meeting in a smaller angle. The basal margin is strongly curved. 

 Externally there are about 12 concentric ribs, each standing on a convex 

 base, the rib and base in section being somewhat like a brace. The whole 

 surface except the summits of the ribs, the lunule and escutcheon, is densely 

 covered with fine radiating striae. The external color is whitish, with purplish 

 brown stains behind and forward of the middle and a number of narrow 

 light brown rays. The anterior dorsal area is somewhat concave and rather 

 broad; escutcheon also sunken, narrower. Interior is white with some brown 

 stains. 



Length 3.4 mm., height 3.3 mm., diameter 1.8 mm. [Pilsbry and 

 Brown, 1932.1 



Range — Cedros Island to the Gulf of California. Mexico: Guaymas 

 (Pilsbry and Lowe): East of Cedros Island; Lower California (Hertlein 

 and Strong). 



Crassinella ecnadorlana, new species Plate 25, figures 6-6e 



Shell small, heavy, oblique, subtrigonal, the posterior side is longer. 



