238 AXEL A. OLSSON 



pale-brown periostracum, sometimes this layer is faintly radially rayed. 

 Hinge as described for the genus. 



Length 10 mm., height 9.1 mm., diameter of a single valve 2.6 mm. 

 Paratype. 



Length 9.7 mm., height 9.3 mm., diameter of a single valve 2.5 mm. 



Holotype, ANSP 218886. 



Range — Peru. Peru: Bayovar on Sechura Bay. 

 Orobitella jipijapa, new species Plate 35, figure 6 



Shell relatively large, oblong-subovate, boat-shaped, inequilateral, the 

 anterior side a little longer and narrower but otherwise the two ends similar, 

 equally rounded, and quite convex. Left valve has a large tooth under the 

 beak bordered behind by the oblique, subumbonal resilifer. Surface with 

 relatively coarse, irregularly raised, threadlike concentrics, the texture some- 

 what chalky. 



Length 12 mm., height 9 mm., diameter 3 mm. (left valve). Holotype, 

 ANSP 218888. 



Much like 0. floridana Dall in shape and sculpture but less inequilateral, 

 the umbone more median in position and the posterior side a trifle longer. 



Range — Ecuador. Ecuador: Puerto Callo, Port of Jipijapa. 



Genus PYTHOELLA Dall, 1899 

 Type species by monotypy, Mysella (Pythinella) cuneata (Verrill and 

 Bush.) {Montacuta cuneata Verrill and Bush). 



Shell small or minute, inequilateral, transversely trigonal with prominent 

 beaks and umbones, the anterior side much the longer, produced, the ventral 

 margin straight or flatly indented. Hinge of Mysella, the right valve having 

 two, well-defined, thickened teeth bordered above by small sockets, and 

 separated by a wide, deep notch under the beak; in the left valve, the hinge 

 is simpler and consists mainly of the bevelled edges or the dorsal margins 

 which fit into the small, grooved sockets of the opposite valve. Ligament 

 principally internal. Surface marked with fine, concentric, growth threads 

 and microscopic, radial striations. Animal probably commensal. 



This group has generally been considered a subgenus of Mysella, but it 

 is so well defined as to warrant generic status. 



Pythinella snblacTls (Carpenter) Plate 36, figure 11; 



Plate 83, figure 12 



Pythina sublaevis Carpenter, 1857, Cat. Mazatlan Shells, Brit. Mus., p. 112, No. 160 



Mazatlan, Mexico. 

 Mysella {Pythinella) sublaevis (Carpenter), Dall, 1899, Proc. U. S. Nat. Museum, vol. 



21, No. 1177, p. 881. 



Shell small, with the characters as described for the genus. The shell 

 is similar to P. cuneata Verrill and Bush taken off Cape Hatteras and may 

 not be specifically distinct. I have a single specimen from shell drift collected 

 at El Lagartillo near Las Tablas, Panama. 



The figure is a reproduction of a camera lucida sketch prepared by 

 Carpenter in the molluscan library at the U. S. National Museum. 



Range— M.tx\co to Panama. Mexico: Mazatlan (Carpenter). Panama: 

 El Lagartillo, near Las Tablas. 



