FOSSILS OF THE NIAGARA GROUP. 



431 



Pentameeus (Pentamerella) ventricosus, Hall. 



(Page 382.) 



I am inclined to regard the P. chicagoensis of W. & M., as only an 

 extravagant form of the above species. Their figure gives five plications 

 on each side, while the specimen (quite imperfect) shows two strong 

 ones in the centre, a much smaller one adjacent on the side ; and outside 

 of this a broad, low elevation, while the third one is not defined by any 

 depression between it and the margin of the shell. 



AVICULA UNO ATA, HaLL. 



(Page 384.) 



This is not to be regarded as a true Avicula, but as having characters 

 so nearly identical with those of that genus, that this reference seemed 

 more proper than any other. The species is not a Pterinea. It has one 

 small anterior tooth in each valve : and an oblique posterior tooth, with a 

 second shorter one in the right valve. The muscular scar is large 

 and subcentral. These characters appear to me more nearly those of 

 Avicula than of Pterinea. The teeth are correctly described by Prof. 

 WiNCECELL as "posterior, linear, diverging teeth," which are quite 

 oblique at the posterior extremity. 



Amphiccelia leidti, Hall. 



(Page 387.) 



The hinge structure of this species will not sanction its reference to 

 Pterinea, made by Profs. Winchell and Marct. The striated hinge- 

 plate mentioned by them, and which I have seen through the kindness 

 of Prof. Marcy, appears as if oblique or expanding outward, giving space 

 for a strong external ligament, while 

 the large pit beneath the beaks does 

 not ally it very nearly with Pterinea ; 

 and until we know more about it, I 

 shall leave it under its proposed gen- 

 eric name of Amphiccelia, though it is 

 scarcely worth while to seek any rela- 

 tion to Leptodomus. In regard to 

 identity with P. neglecta, I have been 

 inclined to the opinion that there 

 may be two species of this genus in 



