375 



Costa Rica Miocene — Olsson 



203 



Subgenus PSEUDAIVSUSIUIVI, H. and A. Adams 



Section PSEUDAMUSIUIVl, s. s. 



Pecten almirantensis, n. sp. Plate 18, figure 16 



Shell small, thin, compressed or but slightly convex; the 

 posterior and anterior dorsal slopes are straight, meeting the 

 beaks at an acute angle; the right valve is finely sculptured with 

 close, regular, concentric lamellae and wider interspaces; the 

 posterior and anterior sides show a few, irregular, radial threads 

 which cross the concentric lamellae; the ears are unfortunately 

 broken; the interior of the shell cavity is filled with a thin de- 

 posit of callus; ventral margin plain; hinge line minutely groov- 

 ed with vertical lines. 



Length 4.75, height 4.75, diameter of right valve 60 mm. 

 This small, elegant species is represented solely by an im- 

 perfect right valve and represent the first true Pseudamusmm to 

 be discovered in the Miocene beds of Panama. Its sculpure is 

 like the recent deep water Pseuda?nusium strigillatai^n Dall from 

 the West Indies, but differs in having its anterior and posterior 

 dorsal submargins meeting at the beaks at a nuicli more acute 

 angle. 



Gatun Stage: Bocas del Toro 



Section CYCLO PECTEN, Verrill 



Pecten Oligolepis Brown and Pilsbry 



Pecten aff. subhyalinus Smith, Toula, 1911, Jahrb. der K-K Geol. 



Reichsanstalt, Wien, vol. 61, p. 492, pi. 31, figs. la, b, c. 

 Pecten {Cyclopecten) oligolepis Brown and Pilsbry, 1912, Proc. Acad. 



Nat. Sci. Phila., vol. 64, p. 512, text-figure 5. 



A very small species with broad, nearly smooth valves and 

 large ears. The right anterior ear has a deep byssal notch and 

 its surface is sculptured with fine, raised, concentric, lamellose 

 lines. The ears of the left valve are similiarly sculptured but fin- 



