145 



Note on the Genus Leptoccelia. 



Among the specimens sent (o me by Dr. Rorninger, are 

 two individuals of Leptoccelia concava, showing the existence 

 of internal spires ; and a careful examination of my own 

 collections from the Lower Helderberg group has shown 

 several specimens possessing these internal organs which 

 have their apices directed obliquely outwards, aud are con- 

 nected near their origin by a strong vinculum on the dorsal 

 side. After repeated examinations of a large number of 

 the Oriskany sand-stone species, from which the characters 

 of the genus were mainly drawn, 1 have failed to detect 

 internal spires. The form of the internal loop as repre- 

 sented in the figures of the genus, was ascertained, as stated 

 by me, mainly from cavities remaining in the crystalline 

 filling of the shell. There were no appearances of spires, 

 nor does a re-examination of the specimen afford any far- 

 ther information, or indicate in any manner that spires 

 have ever existed. The crura can be traced to the division 

 at the process, and below this is a flat cavity. 



A critical re-examination of the fossils referred to this 

 genus, shows that there are at least three distinct types, in 

 their external form and features, which, in the absence of 

 positive knowledge of the internal structure, were grouped 

 together. A farther examination shows some peculiarities 

 of hinge structure in each one of them, which are probably 

 connected with more important difference of the internal 

 parts. One of these types is indicated in the two strongly 

 plicated species of the Oriskany sand-stone, which have a 

 median sinus near the front of the ventral valve, with two 

 of the plications often closed incurved. Another type is 

 that of Leptoccelia concava, and allied forms, which are more 

 finely plicated, and where there is a sinus on the dorsal valve, 

 though not distinctly defined. The third type is repre- 



