c 



ttiENTON LIMESTONE. 217 



ever, has already been said in reference to this part of the subject, and new facts are 

 constantly presenting themselves in favor of the views here advanced, which, from their 

 novelty, and the imperfection and obscurity of many of the specimens, have heretofore 

 been regarded as untenable and unsatisfactory.* 



Position and locality. This specimen is from the valley of West-Canada creek, near 

 Middleville, and in the same position as those previously noticed. {Cabinet of Dr. Emmons.) 



Platb LIX. 

 In the figures 1, 2, 3, I have attempted to give the precise markings presented on the 

 surface of the varieties of E. proteiforme, which are somewhat more distinct than the litho- 

 graphic impressions. 



Fig. 1 a, b. var. ienuitextum. The surface markings on two different specimens, somewhat enlarged 

 beyond the natural size. 



Fig. 2 a, J. var. tenuisiriatum. The surface markings on two different specimens, both slightly mag- 

 nified. A careful examination shows a slight difference in the strength of the markings, 

 which becomes more extreme in other specimens. 



Fig. 3 *. var. lineolalum. This one presents only transverse stricB ; but some specimens show minute 

 longitudinal ones, passing into the preceding variety. 



Fig 3. var. lineolalum. The surface is covered by fine spots or stigmata, as if some adhering softer 

 substance had been separated from it. The same is observed in fig. 2 i, in a less degree. 

 The markings are very similar to the bases of the cells of a Flustra. 



279. 11. ENDOCERAS ARCTIVENTRiJM ( n. sp.). 



Pl. LI. Figs. 2 Oi ft. 



Elongated, very gradually tapering ; septa distant about one third the diameter of the 

 shell ; siphuncle marginal ( ventral ) , slightly contracted at the junction of the septa ; 

 section oval ( probably from compression ) ; embryo tube slender. 



The specimen is a fragment, preserving about eight or nine of the chambers ; but these, 

 with the siphuncle, are different from any other species of this period. The siphuncle is 

 remarkably narrow, somewhat longitudinally wrinkled, and slightly contracted at the 

 junction of the septa. 



The small embryo tube contains a young shell, which has the appearance, in a small 

 portion visible, of Orthoceras junceum ; but this cannot be demonstrated till we obtain 

 other specimens. 



Position and locality. This species occurs, associated with the preceding, in the higher 

 part of the Trenton limestone. 



• This view of the development of the Orthocerata was first imperfectly made known at the meeting of the 

 American Association of Geologists and Naturalists, at Washington, in 1844, and subsequently more fully explained 

 at the New-York meeting in 1846. 



[ Palaeontology.] 28 





