PANAMIC-PACIFIC PELECYPODA 459 



elliptical, the beaks apparently opisthogyrate, placed at the anterior one- 

 third, the anterior side with rather full umbone, its margin well rounded. 

 The posterior side is much longer, somewhat depressed with an obscure 

 carina running from the beak to the posterior-ventral corner. Surface ir- 

 regularly undulated by concentrics which are heaviest on the anterior- 

 umbonal slope. Entire surface coarsely granulose. Pallial sinus short, ex- 

 tending about a third of the distance into the shell cavity. 



Length 34 mm., height 22 mm., semidiameter 6.7 mm. a left valve. 

 Point Ancon, Ecuador. Holotype, ANSP 218955. 



Known only by a single left valve. 



Range — Ecuador. Ecuador: Point Ancon, Santa Elena Peninsula. 



Genus CTATHODONTA Conrad, 1849 

 Type species by monotypy, Cyathodonta undulata Conrad. Gulf of 

 Cahfornia. 



Shell broadly ovate to subrectangular, the anterior side longer, rounded, 

 the posterior side shorter, depressed and subtruncate. Surface sculptured 

 with concentric and sometimes somewhat oblique, wavelike plications or 

 undulations. Surface granulose. 



Cyathodonta undulata peruTiana, new subspecies Plate 83, figures 2-2b 



Cf. Cyathodonta undulata Conrad, 1849, Proc. Acad. Nat. Sci. Philadelpliia, vol. 4, p. 



156. — Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 3, No. 8, p. 96. 

 Cf. Thracia pticata Deshayes, Reeve, 1859, Conch. Icon., vol. 12, rArar/a, pi. 2, figs. 7b, 7c. 

 Cf. Thracia (Cyathodonta) undulata Conrad, Grant and Gale, 1931, Mem. San Diego, 



Soc. of Nat. Hist., vol. 1, p. 259, pi. 13, figs. 6a, 6b. 

 Cyathodonta dubiosa Dall, Durham, 1950, Mem. Geol. Soc. America, No. 43, p. 70, pi. 16, 



figs. 2, 7. Fossil, Lower California. Not C. dubiosa Dall, 1915. 



Shell is subrectangular in shape, rather high, with the height and 

 length in the ratio of four to five, moderately thin and fragile, the umbones 

 and beaks placed slightly behind the middle. Valves are much alike, the 

 anterior side convex and widely rounded at the margin, the posterior side 

 shorter, depressed and more plainly marked. Sculpture is produced by 

 rather coarse, even undulations which on the anterior half of the disk are 

 strongly oblique, crossing the lines of growth; posterior of the middle line, 

 the undulations are concentric to the valve margin, and are lacking com- 

 pletely on the posterior slope. The posterior-umbonal slope and for a space 

 in front of it, there is a relatively wide smooth band extending down from 

 the beak. Entire surface is covered with minute granules arranged in close 

 lines radiating from the beak. 



Length 49.7 mm., height 39.5 mm., semidiameter 9.7 mm. a right valve. 

 Tumbez, Peru. Holotype, ANSP 218953. 



This subspecies differs from typical C. undulata from the Gulf of Cali- 

 fornia by its higher, less elongated form, and especially in having the 

 surface undulations strongly oblique to the lines of growth. It occurs rarely 

 as a Pleistocene fossil in the Peruvian tablazos, I have specimens from 

 the Lobitos tablazo at Malacas, Parinas near Talara, Peru. It appears to 

 be the same form as the shell figured by Durham as P. dubiosa Dall, fossil 

 in Lower California. 



Range — Panama southward to Peru. Panama Canal Zone: Amador; 

 Palo Seco. Colombia: Isla del Gallo. Ecuador: Galeras; Manta; Santa 

 Elena. Peru: Tumbez. 



