TRENTON LIMESTONE. 211 



276. 8. ENDOCERAS PROTEIFORME, var. LINEOLATUM. 



Pl. XLV. Figs. 4 a, b, c, d, e ; Pl. XLVI. Figs. 1 a 6 c, 2 a J, & 3 ; and Pl. XLVII. Figs. 4 a, b, c, d, e. 



Compare Orthoeeratites centralis, Hisinger, Leth. Suecica, 1837, Pl. 9, fig. 4. 



— bacillus, EicHWAU), 1830, Zool. specialis, Vol. ii, pag. 31, pl. 2, fig. 14. 



— — Id. 1840, Sil. Syst. in Esthland, p. 94. 



— linearis, Munstkr, 1840, Beitr. zur Petrefacten, Heft iii, pag. 99, pl. 19, fig. 1 a, b. 



— — D'Archiac & DE Verneuil, 1842, Trans. Geol. Soc. London, New series. Vol. vi, 



part 2, p. 345. 



— bacillus, Verneuii,, 1845, Pal. Russia and Ural Mountains, pag. 353, pl. 24, fig. S a, b. 



This variety is usually more slender than the prevailing forms of the last, but is not 

 essentially different. The surface is marked by fine transverse striae, scarcely visible to the 

 naked eye ; striae somewhat irregular, lamellose, and crowded into bands or fasciae. The 

 sipbuncle is equally excentric with the last, and the septa have a concavity of about one 

 third their diameter ; section circular. 



The length of the fragment fig. 4, pl. 45, is A\ inches ; the comparative diameters of 

 the two extremities are as 4 to 1. In fig. 2, pl. 46, the length is 6^ inches, and the two 

 diameters as 13 to 3, or about the same as in the other specimen. 



The surface of some specimens, when highly magnified, presents very minute or eva- 

 nescent longitudinal striae, approaching in this character to the var. E. tenuistrialum, into 

 which it finally passes by a greater development of the longitudinal striae. The transverse 

 striae are often imbricating, as if produced by the elevated edges of lamellae which are 

 frequently broken or irregular. They also sometimes become vesicular, giving the surface 

 a blotched appearance as in fig. 4 c, pl. 47. Towards the extremity they often become more 

 distinct, and assume the character of sharp annulations. 



This variety differs from the 0. centralis of Hisinger, in the excentric position of the 

 siphuncle, and in the finer striae, in which it approaches to 0. bacillus, which has likewise 

 a central siphuncle and more conical form. 



The finely striated surface of this species is very similar to one or two species in our 

 higher strata ; but in those the striae are usually stronger, and they do not become, in any 

 variety, cancellated in like manner with fine longitudinal striae. It will be desirable, there- 

 fore, to recollect these distinctions, in order to avoid confounding what are really distinct, 

 and from different geological periods. 



Plate XLV. 



Fig. 4 a. A young shell, with the outer chamber and apex broken off This specimen represents the 



prevailing form and dimensions of this variety. 

 Fig. 4 b. Transverse section of the larger extremity of 4 a, showing the position of the siphuncle. 

 Fig. 4 c. A fragment of the smaller extremity of the shell, vi'hich is annulated by fine sharp ridges. 

 Fig. 4 d. The same enlarged. 



Fig. 4 e. A fragment of another tube, marked as fig. 4 a, showing at the lower extremity a septum and 

 siphuncle. 



2T 



