1921] NATURAL SCIENCES OF PHILADELPHIA. 427 



MACTRIDAE. 



Mactra dariensis Dall. 



Madrdla alata Spengler, Gabb, Trans. Amer. Philos., Soc, xv, p. 248. 



Two specimens in hard gray rock, one an internal cast, the other 

 retaining part of the shell, seem to be referable to this species de- 

 scribed from the Ohgocene of the Canal Zone. The best specimen 

 has the sharp grooves on both sides of the beaks described by Dall, 

 and the shape agrees well. 



Gabb's identification was evidently hasty, as little resemblance 

 to M. alata can be traced. 



Labiosa (Raeta) gabbi. Pils. and Johns. Plate XLVI, fig. li. 



Proc. A. N. S. Phila. 1917, p. 202. 



CORBULIDAE. 



Corbula vieta Guppj'. 



Corbula disparilis d'Orb., Gabb, Trans. Amer. Philos. Soc, xv, p. 247. 

 Ccrhula vieta Guppy, Quart. Journ. Geol. Soc, xxii, p. 580, pi. 26, fig. 8. 



Dall, Trans. Wagn. Inst, iii, p. 849. 

 Erycina tensa Guppy, Q. J. Geol. Soc, xxii, p. 582, pi. 22, fig. 6, (left valve). 



Gabb. Trans. Amer. Philos. Soc, xv, p. 252. 



Gabb considered vieta to be identical with disparilis; the resem- 

 blance is certainly great, but according to Dr. Dall, the small 

 differential features are constant. 



Corbula sericea Dall. 



Corbula lavaleana d'Orb., Gabb, Trans. Amer. Philos. Soc, xv, p. 247. 

 Corbula sericea Dall, Tr. Wagn. Inst., iii, p. 848, pi. 36, fig. 8. 



Corbula knoxiana fossilis n. subsp. Plate XLVI, fig. 14. 



Corbula contracta Say, Gabb, Trans. Amer. Philos. Soc, xv, 1873, p. 247. 

 Not of Say. 



The specimens agree well in form with C. knoxiana C. B. Ad. 

 except that the carina projects decidedly less. The type, a right 

 valve, measures length 8.7, alt. 6, diam. 3 mm. 



Type no. 2689 A. N. S. P. 



Corbula dominicensis Gabb. Plate XLVI, flgs. 12, 13. 



Corbula dominicensis Gabb, Trans. Amer. Philos. Soc, xv, 1873, p. 247. 



The right valve is slightly larger. Sculpture of concentric ribs, 

 abrupt on their upper edges, sloping on the lower. On the posterior 

 half the number of ribs is nearly doubled, by spHtting. In the left 

 valve the ribs are simple throughout, not spht posteriorly. 



Ridge to the sharp posterior angle is acute. 



Length 14.6, alt. 9, diam. 6 mm. 



Type is no. 2691 A. N. S. P. 



