PANAMIC-PACIFIC PELECYPODA 127 



Bull. Amer. Mus. Nat. Hist, vol. 107, art. 2, pp 178, 179, pi. 2, figs. 9, 11.— 

 Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 1, p. 64, pi. 6, 

 fig. 29. 



Shell of medium size (length about 50 mm.), relatively thin, elongate. 

 Dorsal and ventral sides straight and subparallel, the posterior side long, 

 inclined towards the base about 30 degrees, forming a produced and nar- 

 rowly rounded end. The anterior side extends a short way beyond the 

 tip of the beak and is obtusely pointed at the tip, A narrowly rounded 

 umbonal slope begins at the beak and extends obliquely backwards to the 

 posterior end, the surface in front and below it a little depressed. Surface 

 smooth except for fine growth lines. Color is pearly white on the 

 anterior one-half and a violet-pink on the posterior side, the division line 

 between the two areas of color lying just below the umbonal angle. In- 

 terior pearly white with the darker color of the posterior surface showing 

 through shghtly. 



Length 50.5 mm., height 19.5 mm., semidiameter 9.3 mm. 



Manta, Ecuador. 



This is a rare species. No trace of a periostracum is shown on any of 

 our specimens. 



Range — Gulf of California to Ecuador. Mexico: Off Mazatlan (Hert- 

 lein and Strong). Ecuador: Off Cabo Pasados (Hertlein and Strong); 

 Manta. 



Modiolus pseudotalipus, new species Plate 14, figures 2, 2a 



Modiolus americanus Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, pp. 67, 68, pi. 

 6, figs. 27, 28; text-figs. 56. (Not of Leach, Ul5=Modiola tulipa Lamarck, 

 1819.) 



Shell oblong, of medium-weight, the umbonal slope full and convex, 

 extending obliquely along the longer axis of the valves from the beaks to 

 the rounded posterior end, the posterior-dorsal and ventral slopes slightly 

 impressed. Anterior side extends a short way in front of the beaks, rather 

 widely rounded at the end. The posterior-dorsal and hinge margins are of 

 nearly equal length, both are straight and set at an angle of about 120 

 degrees to each other. General surface color is a rich brown, deepest on the 

 anterior-ventral surface and on the posterior-dorsal slope with a zone of 

 lighter color extending from the beaks to the middle of the ventral margin. 

 Interior a pearly white tinged with vinaceous. 



Length 64.5 mm.; height 38 mm.; diameter of one valve 13.6 mm. 



Punta Blanca, Ecuador. Holotype ANSP 218956. 



This species resembles the Atlantic Coast M. americanus (Leach), but 

 the posterior side is longer, narrower, the color banding not so sharply de- 

 fined. From M. pacificus, the species differs at all growth stages by its 

 shorter and higher shell and by its more widely rounded anterior end. 



Range — Gulf of Cahfornia southward to Peru. Mexico: Magdalena 

 Bay, Lower California, Mazatlan. Ecuador: Isla la Plata. Punta Blanca. 

 Peru: Negritos; Paita; Yasila. 



Modiolus pacificns, new species Plate 14, figures 3, 3a 



Shell rather large, elongate modioliform, covered with a black brown 

 periostracum which worn off in patches reveals a nearly white shell un- 



