280 AXEL A. OLSSON 



Agrlopoma (Pitaxella) mexloana (Hertleiu and Strong) 



Pitar lenis Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 84, p. 100, 

 pi. 16, fig. 6 Acapulco, 20 fms., also Guaymas, 20 fms. (Not Pitaria lenis 

 (Conrad) (as Cytherea lenis Conrad, 1848).) 



Pitar (Pitarella) mexicanus Hertlein and Strong, 1948, Zoologica, vol. 33, pt. 4, pp. 171, 

 172, pi. 1, figs. 3, 8. 



Shell elongately oval, rather thin, white, exteriorly resembling Comp- 

 somyax subdiaphana (Carpenter); ornamented with close, fine, concentric 

 riblets over the whole valve or subobsolete medially; lunule large, cordate, 

 bordered by an incised line; hinge of left valve with 3 cardinals and an 

 anterior lateral tooth, the anterior and middle cardinals are joined dorsally, 

 the middle one is longer and thicker, a pit occurs at the base, the posterior 

 cardinal is elongate and thin, the lamella forming the middle and anterior 

 cardinals bears slight irregularities or cusps, the anterior lateral with 2; 

 hinge of right valve with a high thin anterior cardinal connected with a 

 bifid posterior cardinal, the middle cardinal is separated from the anterior 

 cardinal by a narrow space but separated from the posterior cardinal by a 

 much wider space, anteriorly there are two low laterals separated by a pit; 

 pallial sinus short, wide, ascending, rounded at the end. Dimensions: length 

 42.3 mm.; height 33.3 mm.; convexity (both valves together), 25 mm.; 

 pallial sinus projects forward approximately 20 mm. from the posterior 

 margin. Holotype (Calif. Acad. Sc. Paleo.). 4 miles south-southwest of 

 Maldanado Point, Mexico in 26 fthms. (Hertlein and Strong, 1948.) 



This species differs from A. catharia by its longer posterior side. When 

 small, the posterior-ventral margin is often slightly insinuated; such a small 

 shell was figured by Pilsbry and Lowe under the name Pitar lenis (pre- 

 occupied by Conrad); a small shell of this type is in my collection from 

 the Pleistocene of Rabo de Puerco, Puerto Armuelles, Panama. Hertlein 

 and Strong give many stations for this species north of Panama. 



Range — Gulf of Cahfornia to Ecuador. Ecuador: Esmeraldas. 



Genus TEANSENNELLA Dall, 1883 

 Type species by monotypy, Transennella cowradina Dall. Recent, 

 Florida. 



Shell usually small, subtrigonal to subovate, subsolid, smooth and 

 polished or concentrically sculptured. Hinge with three cardinal teeth in 

 each valve; an anterior lateral tooth is present in the left valve and received 

 in a lateral socket in the right. Lunule subelliptical, defined by a small, 

 incised line, no escutcheon. Nymph narrow and smooth. Pallial sinus angular, 

 extending into the interior about a third. Inner margins of valves without 

 crenulations but grooved tangentially with numerous incisions or sulci. 



A genus composed mostly of small species, recognized readily by the 

 small incised lines or grooves which cut across the ventral margins tangent- 

 ially or in an oblique direction. 



Transennella modesta (Sowerby) Plate 46, figures 4-4b 



Cytherea modesta Sowerby, 183S, Proc. Zool. See. London, p. 47 Xipixapi. — Sowerby, 

 1851, Thes. Conch., vol. 2, p. 627, pi. 136, fig. 184 (as Cytheraca). 



