PANAMIC-PACIFIC PELECYPODA 173 



Shell elongate arcuate, (length up to 100 mm.), the two valves nearly- 

 alike, ventral margin folded into three or four large, sharp but short plica- 

 tions, attached generally by a small area on the extreme umbone of the left 

 valve. The dorsal side is concave or excavated, often finely corrugated 

 on the margin. Surface smoothish or roughened by concentric growth in- 

 cremental. Color white or green, tinged with violet or purple. Lateral 

 margins finely crenulated. 



Closely related forms occur in the Miocene of northern South America, 

 Costa Rica, Santo Domingo, and Florida, but the group is extinct in the 

 Caribbean area. It is a common fossil in the Peruvian tablazos. 



Range — Gulf of California to northern Peru. Costa Rica: Opposite 

 Judas Point (Hertlein and Strong), Ecuador: Atacames. Peru: Bay of 

 Sechura. 



Ostrea (Alectryonia) palmula Carpenter Plate 17, figures 6. 6a; 



Plate 23, figures 5, 5a, 7, 7a 

 Ostrea ft conchap/iila var. palmula Carpenter, 1857, Cat. Mazatlan Shells, Brit. Mus., 



pp. 163, 550. 

 Ostrea mexicana Sowerby, 1871, in Reeve, Conch. Icon., vol. 18, Ostrea, pi. 16, figs. 



35a, b, c. 

 Ostrea palmula Carpenter, Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, pp. 



55, 56, pi. 1, fig. 14. 



Shell comparatively small, heavy, irregular in form, the lower valve 

 usually deep, strongly ribbed beyond the area of attachment and closely 

 attached by a large part of its surface to rocks and the like. The upper 

 valve is usually flat and depressed in the middle, becoming plicate around 

 the margin. Color a dirty or greenish white veined with violet. Interior 

 is mostly white, the marginal band brown or violet, the adductor scars 

 white or with brown and violet staining. Inner margin of shell is dentic- 

 ulate all around in the upper valve, less so in the lower. 



This species seems to be fairly abundant at many locations, usually 

 firmly attached to rocks exposed to heavy surf. It is too small for any 

 economic importance as a food. 



Range — ^Gulf of California southward to Ecuador and the Galapagos. 

 Panama: Panama City; Guanico. Ecuador: Camarones near Esmeraldas. 



Ostrea (Alectryonia) fischerl Dall Plate 23, figure 6 



Ostrea jacobaea Rochebrune, 1895, Bull. Mus. Nat. Hist. Nat. Paris, vol. 1, p. 241. (Not 



O. jacobaea Linne. 

 Ostrea fischeri Dall, 1914, Nautilus, vol. 28, No. 1, p. 1. (Nevvr name to replace O. 



jacobaea Rochebrune). — Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, 



pp. 54, 55. — Durham, 1950, Mem. Geol. Soc. America, No. 43, pt. 2, p. 59, pi. 



6, figs. 1, 4. 



Shell large (length 120 mm.), subcircular to obliquely oblong, thick, 

 generally strongly plicated with six or more heavy ribs and sharp folds, 

 heaviest near the margin, similar in both valves. These ribs occasionally 

 develop irregular hollow tubular extensions. Color violet red to dark purple, 

 the interior white except for some brown staining. Adductor scars large, 

 placed slightly posterior of the middle. Cardinal area wide and heavy. 

 Substance of the shell is thick, made up of porcellaneous layers interfingered 

 with porous and cellular seams. 



This large oyster is closely related to several fossil species from the 

 Caribbean and Floridan area such as 0. haitensis Sowerby from the Miocene 



