375 Costa Rica Miocene — Olsson 203 



Subgenus PSEUDAiViUSIUIVl, H. and A. Adams 



Section PSEUDAMUSIUIVI, 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 solel}^ by an im- 

 perfect right valve and represent the first true Pseudaniushi7n to 

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

 like the recent deep water Pseudajiiusiwn strigillatjnn Dall from 

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

 dorsal submargins meeting at the beaks at a much more acute 

 angle. 



Gatun Stage: Bocas del Toro. 



Section CYCLO PECTEN, Verrill 



Pecten Oligolepis Brown and Pilsbry 



Pecten aff. siibhyalinus 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- 



