PANAMIC-PACIFIC PELECYPODA 353 



Shell small, elongate, thin, and subtranslucent, its general color white 

 flushed with violet and with two small, oblique, white rays extending across 

 the umbones backwards. Dorsal and ventral margins subparallel, straight, 

 except for a slight inbend of the ventral margin due to a flattening of the 

 surface of the valve across the middle. The internal thickened ray is usually 

 strong, dark-purple in color and extends a little below the middle either 

 vertical or inclined slightly posteriorly; it shows through the substance of 

 the shell as a dark streak on the umbone; behind it there are two white 

 rays which extend obliquely downward to the posterior portion of the 

 ventral margin. The largest specimens attain a length of about 40 mm. 



Range — ^West Mexico to northern Peru. Panama: Bucaro. Colombia: 

 Isla del Gallo. Ecuador: Santa Elena. Peru: Tumbez. 



Tagelus (Mesopleura) pernyianns Pilsbry and Olsson Plate 62, figures 3-3d 



Tagelus {Mesopleura) peruvianus Pilsbry and Olsson, 1941, Proc. Acad. Nat. Sci. 

 Philadelphia, vol. 93, pp. 70, 71, pi. 18, fig. 5.— Hertlein and Strong, 1950, 

 Zoologica, vol. 35, pt. 4, p. 224. — Hertlein and Strong, 1955, Bull. Amer. Mus. 

 Nat. Hist., vol. 107, art. 2, pp. 202, 203. 



Shell elongate, its height about a third of its length, of moderate con- 

 vexity, the small beak not central, the posterior end is a trifle longer. Ven- 

 tral margin straight, the dorsal a little arched on the anterior side, notice- 

 ably winged on the posterior. The shells are usually a little warped in the 

 middle which accentuates the gap at the ends. Young shells are thin and 

 translucent on removal of epidermis and show the thickened ray of Meso- 

 pleura directed slightly backwards, but in the adult this ray may disappear 

 entirely or show only as a slight thickening of this part of the shell. Pallial 

 sinus ample, rounded, higher within the shell than at its opening, and 

 extends not quite to the middle. Color in most specimens is white shaded 

 with brown or violet and with a colored streak over the internal ray or its 

 location, and there are two narrow, white rays over the umbones. The 

 periostracum is coarsely wrinkled and dark-brown in color. 



Length 82.6 mm., height 79.6 mm., diameter 15.8 mm. Puerto Callo, 

 Ecuador. 



This is a common Pliocene fossil in Ecuador. It is easily distinguished 

 from all other Pacific Coast tageUds by the flangelike wing on the posterior- 

 dorsal margin. Like T. dombeii in surface coloration but with more elongated 

 valves. 



Range — Gulf of California to northern Peru. Panama: Guanico. Ecua- 

 dor: Galeras; Manta; Puerto Callo; Santa Elena. Peru: Tumbez; Mancora; 

 Zorritos. 



Tagelus (Mesopleura) bourgeoisae Hertlein 



Tagelus {Mesopleura) bourgeoisae Hertlein, 1951, Bull. South. California Acad. Sci., 

 vol. 50, pt. 2, pp. 73, 74, pi. 26, figs. 5, 6. 



This species was described by Hertlein from specimens collected at 

 Santa Cruz, Mexico. It is distinguished from other allied species (such as 

 T. politus Carpenter) in that the internal rib slopes anteriorly rather than 

 posteriorly. The species was also recorded by Hertlein from Santa Elena, 

 Ecuador, but I have not seen specimens. 



Range — Mexico to Ecuador. Ecuador: Santa Elena (Hertlein). 



