PANAMIC-PACIFIC PELECYPODA 131 



anterior, hence, the dorsal and ventral margins appear to slant in towards 

 each other anteriorly. Beaks almost terminal, and from which the umbonal 

 axial slope extends full and convex to the posterior-ventral corner of the 

 valves. The posterior-dorsal margin is long and straight, the posterior 

 margin widely rounded, the ventral margin narrow and nearly straight. 

 Surface sculpture consists of small riblets separated by narrow, cancellate 

 interspaces, the riblets divaricating along the umbonal axis, simple on the 

 anterior-umbonal slope; there is in addition a line of demarcation separ- 

 ating the central zone of sculpture from that on the anterior-ventral side 

 and another line of separation from the posterior-dorsal zone. 

 Length 2.2 mm., height 2.3 mm. 



Distinguished easily from C. ecuadoriana by its unsymmetrical valves 

 and subrhombic shape. 



Range — Ecuador. Ecuador: Santa Elena. 



Genus BOTULA Morch, 1853 



Type species by subsequent designation, Dall, Bartsch and Rehder, 

 1938. Mytilus juscus Gmelin. Caribbean. 



The shell is small or of medium size, oblong, subrhomboidal, arcuate, 

 modioliform, convex, the surface covered by a glossy brown periostracum. 

 The umbones are prominent and full, ending in small, coiled beaks re- 

 moved sHghtly from the anterior margin and projecting beyond them. 

 Surface sculpture is formed principally by weak concentric growth lines 

 or their derivatives, interrupted by deeper resting marks, and occasionally 

 iby a few obscure radials over the middle ventral zone. Hinge line straight, 

 edentulous, the resilifer internal and showing as a long scar nearly the 

 length of the hinge line. Interior bluish nacreous. Adductor scars subequal 

 in size, rounded or gourd-shaped, placed low within the shell and near the 

 margins. 



Botnla fiisca (Gmelin) Plate 16, figures 5-5c 



Mytilus fuscus Gmelin, 1791, Systema Naturae, ed. 12, p. 3359. 



Lithophagus cinnamomeus (Chemnitz), Carpenter, 1857, Cat. Mazatlan Shells, Brit. 



Mus., p. 129 Mazatlan, Mexico. Not of Lamarck, 1819. 

 Botula cinnamomeus (Chemnitz), Strong and Hanna, 1930, Proc. California Acad. 



Sciences, sen 4, vol. 19, No. 3, p. IS Tres Marias Islands, Mexico. 

 Lithophaga (Botula) fusca (Gmelin), McLean, 1951, Scien. Survey of Porto Rica and 



the Virgin Islands, New York Acad. Sciences, vol. 17, pt. 1, p. 43, pi. 8, fig. 3. 

 Botula fusca (Gmelin), Soot-Ryen, 1955, Allan Hancock Pacific Expeditions, vol. 20, 



No. 1, p. 86, pi. 9, fig. 52; text-figs. 70-72. 



Shell as described for the genus. A single specimen was obtained at 

 Manta where it was found in a rock burrow and like Musculus coarctata, 

 is possibly a true rock borer. The two species live in the same environment. 

 My specimen agrees well with typical B. fusca from the Caribbean. It 

 agrees also with the figure of B. hazvaiensis Dall, Bartsch, and Rehder 

 as illustrated in their Hawaiian paper. The color of the surface is a dark 

 brown to nearly black. 



Length 22.5 mm.; height 10.5 mm.; diameter 9.6 mm. 



Manta, Ecuador. 



Range — Mostly West Indies and the Caribbean; on the Pacific Coast 

 from Mexico to Ecuador (rare). Ecuador: Manta. 



