310 PALJBONTOLOOy OF NEW-YORK. 



370. 2. TROCHOLITES PLANORBIFORMIS. 



Pi- LXXXIV. Figs. 3 a, J, c, d, e,/. 

 TrotholiUt planorbiformU. Conrad, Jour. Acad. Nat Sciences, 1842, Vol. viii, pag. 274, pi. 17, fig. 1. 



Depressed, orbicular, or planorbiform ; volutions about four or five, wider than deep ; 

 apex profoundly and equally depressed on both sides ; aperture Innate ; section elliptical, 

 with the inner side concave from the junction of the next volution ; surface marked by 

 obliquely transverse ridges, which bend backwards, forming a broad curve on the dorsal 

 line, longitudinally striated with rounded lines. 



In all the specimens examined, the outer lamina of the shell is exfoliated, and the fine 

 etriee of the surface are destroyed. The character of the shell is much like that of T. am- 

 monius, and I have been disposed to regard it as a variety of the same. But in specimens of 

 that species from the Trenton limestone, I have rarely found the transverse and longitudinal 

 ridges so strongly marked as in this specimen. The shell is always larger than the specimens 

 of the Trenton limestone, but in other respects there are few important differences ; and it 

 presents no greater variety than is represented in the Lituites cornuarietis, by Murchison 

 and DE Verneuil. 



Fig. 3 a. Figure of a speciraeu nearly entire. 



This figure is given from an imperfect specimen, the parts wanting being supplied from 



the figure of Mr. Conrad, the- original of which I have examined in the cabinet of the 



Academy of Natural Sciences, at Philadelphia. 

 Fig. 3 b. Dorsal view of the same. 

 Fig. 3 e. Ventral view of a fragment, preserving part of the two outer volutions, showing the concave 



ventral side, and the position of the siphuncle. 

 Fig. 3 d. A. portion of the surface magnified. 

 Fig. 3 e. A specimen crushed in a vertical direction ; a part of the outer volution retaining its form in 



a sufficient degree to identify the species, 

 Fig. 3/ Dorsal view of the same, showing the slightly arching septa upon the dorsal line, and a part 



of the outer chamber. 



Nearly all the specimens found in the Hudson-river group, in New- York, are crushed 

 and distorted. The single perfect specimen known to me, with another less perfect, were 

 obtained near Grimsby, Canada West, by Mr. Ashmead of Philadelphia. 



Position and locality. This species occurs in the central part of the group at Turin in 

 Lewis county, Pulaski in Oswego county, and several other localities. The specimens from 

 Canada are associated with other fossils peculiar to this group, leaving no doubt of their 



position. {State Collection.) 



