TRENTON LIMESTONE. 195 



which bend abruptly downward over the dorsal line, in form like the letter V. The 

 siphuncle is also dorsal. 



Tig. 1 a. A frag'raent, showing a partial section. 



Fig. 1 i. A large fragment, showing the wide outer chamber. 



Fig. 1 c. Section of the smaller extremity of the last. 



Fig. 3 a. Dorsal view of a fragment probably identical ; the striae in the figure do not bend so abruptly 



as in the original. ,s 



Fig. 3 b. Lateral view of the same. 



Position and locality. In the Trenton limestone at Middleville ( N. Y.), Carlisle (Pa.), 

 and in light buff-colored limestone of the same age at Mineral Point ( Wisconsin) . 



( state Collection ; Cabinet of Mr. Conrad.) 



253. 4. CYRTOCERAS CONSTRICTOSTRIATUM (n. 5p.). 



Pi,. XLII. Figs. 2 a, b, and 3 c, d. 



Very gradually curving, and enlarging towards the aperture, which is but little 

 expanded 5 septa approximate ; siphuncle dorsal ; surface marked by filiform transverse 

 striae, which, at intervals, are bent abruptly downwards, or constricted ; section elliptical. 



This species, from its very slight curvature and gradual tapering, might perhaps be 

 regarded as an Orthoceras ; from which, however, I believe it to be distinct. I have relied 

 mainly on the external markings to characterize the species, but have arranged with the 

 one thus marked, other fragments, which appear to me of the same species, though 

 destitute of the shell. 



Fig. 3 c. A fragment, showing the surface markings. 



Fig. 3 d. Section of the same, which does not show the siphuncle. 



Fig. 2 a. A fragment, showing several of the septa and a part of the outer chamber. 



Fig. 2 b. Transverse section, somewhat compressed, showing the position of the siphuncle. 



Position and locality. This species usually occurs in fragments in the lower shaly layers 

 of the Trenton limestone at Middleville. A single specimen, o°ly> has been found in the 

 upper part of the rock at the same place. 



254. 5. CYRTOCERAS MULTICAMERATUM (n. si9.). 

 Pl. XLII. Fig. 4. 

 This specimen is a fragment denuded of the shell ; it is somewhat straight above, more 

 abruptly curving below, and gradually tapering. It is remarkable for the close approxima- 

 tion of the septa. 



The specimen is too obscure and imperfect to be reliable, but is given as clearly showing 

 its distinction from the other species. 



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



{State Collection.) 

 25* 



