TKENTON LIMESTONE. 205 



270. 23. ORTHOCERAS AMPLICAMERATUM (h. «jj.). 



Pl. LI. Figs. 1 a- g. 



Teretely cylindrical, extremely elongated, very gradually tapering; outer chamber 

 profound ; septa distant about one third the diameter, very convex ; siphuncle excentric, 

 small; surface 1 section circular. 



The peculiarities of this species arc its great length, and very gradual diminution from 

 the larger extremity, and the distant and very convex septa, which seem sufficient to 

 distinguish it from all other species known in this rock. 



In all the specimens examined, there is no enlargement of the siphuncle sufficient to 

 admit the development of embryo tubes, unless they are mainly confined to the outer 

 chamber, a longitudinal section of which does not reveal any thing of that kind. 



Fig. 1 a, b. Parts of the same individual, preserving a large portion of the outer chamber, with an equal 



length of the septate part of the tube. 

 Fig. 1 c. A transverse section of the specimen, at the upper e.xtremity of 1 a, showing the excentric 



position of the siphuncle. 

 Fig. y d, e. A fragment of another specimen, showing the same distance of the septa and excentric 



position of the siphuncle. - - 



Fig. 1 / A fragment of the septate portion of a much larger specimen. 

 Fig. 1 g. Transverse section of the same, showing the position of the siphuncle. 



Position and locality. This species is found in the central and Iiigher part of the Trenton 

 limestone at Middleville. (State Collection.) 



271. 24. ORTHOCERAS STRIGATUM (». 5/;.). 



Pl. LVI. Figs. 1 a, b, c, d. 

 Compare O. lineatum, Hisinger, pag. 29, pl. 9, fig. 6. 



Elongated, teretely cylindrical, gradually tapering ; outer chamber large ; septa distant 

 about one fifth the diameter of the shell, very convex ; siphuncle small, central ; surface 

 marked by flexuous elevated longitudinal lines, which are indistinctly visible on the cast. 



In the comparative distance of the septa, this species approaches some of the varieties of 

 Endoceras proteiforme ; but the septa arc more convex, and the siphuncle always central. 

 The longitudinal stria difTer essentially from the ridges in the next species, and are more 

 distinct than in any of the species witliout annulations. The transverse stria;, if any exist, 

 are mucji finer, and not preserved where the shell is exfoliated. 



This species approaches in character to the O. lineatum o[ Hisinger ; but the longitudinal 

 stria; are stronger than in that species, judging from (he character of the smface, whicli is 

 imperfectly preserved in our specimens. 



