TRENTON LIMESTONE. 193 



There may be some doubt as to the propriety of separating this species from Lituites, 

 which has been done principally on account of the ventral position of the siphuncle ; since 

 this deviation is not usually regarded as important. M. de Verneuil, speaking of this 

 position of the siphuncle in L. odini, does not consider it as sufficient to found a generic 

 distinction. 



Fig. 4 ffi. A small perfect specimen, showing the lamellose striae in great perfection.  



Fig. i b. A large specimen, preserving the lamellose surface. 



Fig. 4 c. Dorsal view, showing the archings of the striae upon the back. 



Fig. 4 d. A specimen denuded of the shell, showing the septa and deep outer chamber. 



Fig. 4 e. Section, showing the position of the sipliuncla 



Fig. if,g. Lateral and dorsal view of a fragment of an inner volution, showing a shght undulation of 



the septa on the back. 

 Fig. 4 A. Lateral view of a fragment partially denuded of the shell, showing only the oblique transverse 



ridges. 

 Fig. 4 i. Dorsal view of the same, showing the arching of the striae upon the back. 

 Fig. 4 k. Section of the same, showing the position of the siphuncle. 



Position and locality. This shell occupies a central position in the Trenton limestone, 

 being unknown in the lower part, but passing upwards into the Utica slate, where it is of 

 less frequent occurrence. {,State Collection.) 



250. 1. CYRTOCERAS LAMELLOSUM (n. SJ9.). 



Pl. XLI. Figs. 2 a, b, e. 



Subcylindrical, gradually curving and tapering ; aperture somewhat expanded, and the 

 shell slightly constricted just behind ; septa closely arranged ; surface with transverse 

 undulating squamose lamellae, which are abruptly bent backwards on the dorsal line ; 

 lamellae equidistant with the septa, but not corresponding to them ; spaces between the 

 lamellae marked by fine transverse striae. 



The form of the entire shell is unknown, the only specimen seen being a fragment : 

 this, however, is weir characterized in its surface markings, which resemble in some 

 degree those of the Cyrtolites compressus ; but the lamella are more squamose, and less 

 abruptly undulating, as well as more closely arranged than is usual in that species. An 

 exfoliation of the shell on one side exposes the interior, which is clearly septate. 



Fig. 2 a. Lateral view of the fragment 



Fig. 2 b. Dorsal view of the same. 



Fig. 2 c. Magnified portion of the surface. 



Position and locality. In the lower part of the Trenton limestone at Middleville. 

 [Palaeontology.] 25 



