5 1 2 



PROCEEDINGS OF THE ACADEMY OF 



[Dec, 



a dense and minute sculpture of raised concentric threads or growth- 

 laminae, which are not emphasized in passing over the striae. 



Length 62, altitude 57, semidiameter 13 mm. 



Reventazon River, Costa Rica, Type a right valve. Collected 

 by Win. M. Gabb, Coll. A. N. S. P. 



This specimen was referred by Gabb to P. paranensis Orb., which, 

 while doubtless related, differs decidedly in the secondary sculpture. 

 We are equally unable to refer the Costa Rican species to P. 7nadi- 

 sonius, which has higher and usually fewer ribs. The Santo 

 Domingan specimens which Gabb identified as the unfigured P. 

 oxygonum Sowb. are all smaller than the present shell, with some- 

 what more elevated ribs, which bear fewer radial striae. 



Dall has proposed a Pecten gabbi s for specimens from Antigua 

 and Santo Domingo, which have the general form of this shell, but 

 differ by having "narrower interspaces each filled with one imbri- 

 cated riblet." In P. optimum there are 4 or 5 striae in each interval, 

 and when one is larger it is not conspicuously so. Dall includes 

 Gabb's Costa Rican shell in his references, but does not refer to it 

 in the text. Gabb does not report paranensis from Santo Domingo. 



Pecten (Cyclopecten) oligolepis n. sp. Text fig. 5. 



Pecten app. subhyalinus Smith, Toula, J. B, dor k.k. Geolog. Reichsan- 

 stalt, 1911, Bd. 61, p. 492, pi. 31, figs, la, b, c. 



This shell is very close to the West Indian Cyclopecten simplex 

 Yerrill, but differs in details of sculpture. The right valve has 



concentric sculpture of excessively 

 faint and fine striae, scarcely visible, 

 and only under the compound mi- 

 croscope, and there are slightly more 

 distinct radial threads near the edges. 

 The left valve has rather widely 

 spaced low concentric threads and 

 more delicate radial threads, chiefly 

 seen near the margins. In C. simplex 

 the right valve is the more strongly 

 sculptured, according to Verrill. The 

 internal structure is substantially as figured for C. simplex (Trans. 

 Conn. Acad., X, pi. 19, figs, 1, 2). 



Length 2.8 ; height 2.7, diam of right valve .8 mm. 

 From the excavation of the lower locks at Gatun. 



Fig. 5. 



:: Trans. Wagner Free Inst. Sci., Ill, p. 717, pi. 29, fig. 3. 



