TERTIARY FOSSILS. 55 



Hemimactra, since, from the nature of the matrix, I have found it impossible to 

 expose the hinge. 



PSEUDOCARDIUM, Gabb. 



By an unfortunate coincidence, Mr. Conrad indicated a genus Pseitdocardia, of 

 the family Cardiidce almost simultaneously with my publication of the above 

 name. My genus was published February, 1866, while Mr. Conrad's appeared in 

 the Journal of Conchology for April, 1866. It is questionable whether a name 

 should stand when it only ditfers from an older one by the terminal letter, though 

 Mr. C. assures mo that he sees no reason for changing it. I merely wish to call 

 attention to the matter here, in order to guard against confusion, which might pos 

 sibly arise in the future. In this case Mr. Conrad publishes no semblance of a 

 diagnosis, merely giving a list of species belonging to the proposed genus. 



VENUS, L. 

 V. PERTENUIS, Gabb. 



( V. pertenuis, G. Pal. Cal., Vol. 2, p. 22, pi. 5, fig. 37. Note.) 

 (V. Kennerleyi, Eve. ? G. loc. cit.) 



"When first studying this species, I was unacquainted with Reeve's V. Kennerleyi, 

 and had not access to his monograph in Icon. Conch. The short notes by Carpenter 

 in the Report of the British Association, were not inapplicable to the shell before 

 me, but were not sufficiently explicit to enable me to satisfy myself as to its dif 

 ference from Kennerleyi. On looking at the figure in Icon. Conch. I find that 

 there are strong points of difference. V. (Mercenaries) Kennerleyi is an elongate, 

 oval, almost quadrate shell, with heavy ribs, pretty regularly placed, and remark 

 ably prominent. It resembles somewhat a Saxidomus in outline, while the present 

 species is a sub-triangular shell, the surface undulated and striate, but without ribs, 

 properly speaking. It is very probable that pertenuis may prove to be a Chione. 

 I have never yet been able to expose the hinge. A large specimen of Mercenaries 

 perlaminosa, Con., now before me, resembles so nearly Reeve's figure in both out 

 line and the character of the ribs, that I strongly suspect them of being identical. 

 In the present specimen (see pi. 15, fig. 14), the ribs are not more than half as nu 

 merous as in the one figured in Pal. Cal, Vol. 2, fig. 38 ; the shell is more elongate 

 in its antero-posterior diameter, and the base is much less rounded. On collecting 

 a series of this species at Santa Barbara, where it is not rare, I found that the pres- 



