412 PROCEEDINGS OF THE ACADEMY OF [PaRT II 



Peten augusticostatus Gabb, Plate XLV, figs. 7, 8. 



Pecten augusHcostatus Gabb, Trans. Amer. Philos. Soc. xv, 1873, p. 256. 



The sole specimen of this species is a left valve. It has 22 ribs. 

 These are very high and acute, in section like an inverted V. Their 

 slopes and intervals have an extremely fine, regular raised concentric 

 striation. The anterior submargin has several very low ribs, and 

 there are a few delicate riblets on the adjacent ear. 



Length 24.3, alt. 23.8, convexity 8 mm. 



Type no. 2866 A. N. S. P. 



While this species is closely related to the preceding, it should 

 be retained distinct until connecting specimens are found. It 

 differs by the more numerous, far sharper ribs, the low ribs on the 

 anterior submargin, the greater convexity, and the finer concentric 

 striation. 



There cannot be much doubt that the name as printed is an 

 error for angusticostatus. Gabb was in Costa Rica when his paper 

 was printed, and did not see the proofs. 



Pecten uselmae Pils. and Johns. Plate XLV, flg. 9. 



Proc. A. N. S. Phila. 1917, p. 194. 



Bowden, Jamaica. Type no. 11124 A. N. S. P. 



Pecten inaequalis Sowerby. Plate XLV, fig. 11. 



Pecten inaequalis Sowerby, Q. J. Geol. Soc, vi, 1849, p. 52. Not P inaequ- 

 alis of Guppy or of Dall. 



This is an abundant Aequipecten in the collection. It is nearly 

 equilateral, distinctly inequi valve. There are rounded ribs and 

 concave intervals in both valves, the ribs in the left valve as wide 

 as the intervals, in the right valve decidedly narrower. The great- 

 est number of specimens have 19 ribs; many have 20 and the ex- 

 tremes, represented by a few, are 18 and 22 ribs. A very fine con- 

 centric sculpture of hair-like threads runs over both ribs and in- 

 tervals, but is usually a good deal worn. 



Length 38.5, alt. 37.3 mm. 



The figures represent both valves of one individual. So far as we 

 know, the species has been found only in Santo Domingo. 



Pecten eccentricus Gabb. Plate XLV, flg. 12. 



Pecten eccentricus Gabb, Tran.s. Amer. Philos. Soc, xv, 1873, p. 256. 



Pecten {Plagioctenium) excentricus Gabb, Dall, Trans. Wagn. Inst., iii, p. 717. 



This species is distinctly inequilateral. The type has 21 ribs, 



separated by wide, rather shallow intervals, and sculptured with 



very fine, close concentric threads, mainly lacking anteriorly. The 



