CLINTON GROUP. 



103 



The three following species were found in a loose mass of gray sandstone evidently belonging 

 to the Clinton group, but whether to the upper gray sandstone, can not well be determined at 

 the present time. 



500. 3. PENTAMERUS OVALIS. 



Pl. XXXI. Tig. 1, 1 a. 



Dorsal valve more or less elongated, varying from nearly circular to elliptical ; larger in- 

 dividuals becoming sub-trilobate ; the specimens which are casts, preserving some remains of 

 concentric strise. 



This species approaches in character to the P. oblongus of the lower limestone of this group, 

 but it is evidently a much smaller shell, and differs in other essential features from that species. 

 The P. oblongus likewise occurs in the same neighborhood, but in a much lower position, cor- 

 responding to its horizon in Wayne and Monroe counties ; while the upper sandstone holds a 

 much higher position, corresponding probably to the upper limestone of the group on the 

 Genesee river, where the whole is much diminished from its thickness in Oneida county. 

 This species seems to be restricted to its lower position in all the localities known. 



Fig. 1. A small valve, having a width slightly greater than the length. 



Fig. 1 a. A larger valve, having a length nearly once and a half the width. The shell is re- 

 moved, though the cast still preserves some slight markings of strise or lines of 

 growth. 



Position and locality. In a loose mass of gray sandstone of the group, New-Hartford, 

 Oneida county. 



446. 21. LEPT^NA OBSCURA? 



Pl. XXXI. Fig. 2. 

 Reference pag. 62, pl. 21, fig. 6 a, b. 

 The specimen figured is a cast in sandstone, which presents no reliable characters to distin- 

 guish it from the species before figured under this name. The strise are represented too strong 

 and coarse in the present figure, which has arisen in part from the character of the sandstone 

 preserving the surface of the cast. 



Position and locality. In a loose mass of gray sandstone of the Clinton group, New- 

 Hartford, Oneida county. 



501. 1. PLATYOSTOMA*. 



Pl. XXXI. Fig. 3 a, b. 

 Sub-globose, depressed ; volutions about three, rapidly increasing towards the aperiure, 

 which is much expanded ; surface marked by simple uninterrupted striae. 



* Platyostoma, Cunrad; Naticopsis, M'Coy. I am unable, from the descriptions and figures given by Mr. 

 Conrad, and those given by Mr. M'Coy, to find any sufficient characters to distinguish Platyostoma from Nati. 

 copsis. I have therefore preferred to adopt the former genus, since it has precedence in point of time, and wa« 

 applied originally to fossils well known to us in the rocks of New-York, 



