TRENTON LIMESTONE. 
211 
276. 8. ENDOCERAS PROTEIEORME, var. LINEOLATUM. 
Pl. XLV. Figs. 4 a , b , c , d , e ; Pl. XLVI. Figs, laic, 2 a b , & 3; and Pl. XLVII. Figs. 4 a , b , c , d , e . 
Compare Orthoceratites centralis , Hisinger, Lcth. Suecica, 1837, Pl. 9, fig. 4. 
— bacillus , Eichwald, 1830, Zool. specialis, Vol. ii, pag. 31, pl. 2, fig. 14. 
— — Id. 1840, Sil. Syst. in Esthland, p. 94. 
— linearis , Munster, 1840, Beitr. zur Petrefacten, Heft iii, pag. 99, pl. 19, fig. 1 a , b . 
— — D’Archiac & de Verneuil, 1S42, 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. 8 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 stria?, scarcely visible to the 
naked eye ; striae somewhat irregular, lamellose, and crowded into bands or fascia?. The 
siphuncle 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 4j inches ; the comparative diameters of 
the two extremities are as 4 to 1. In fig. 2, pl. 46, the length is 5^ 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 mag'nified, presents very minute or eva¬ 
nescent longitudinal stria?, approaching in this character to the var. E. tenuistriatum , into 
which it finally passes by a greater development of the longitudinal stria?. The transverse 
stria? are often imbricating, as if produced by the elevated edges of lamella? 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 he 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 , shoiving the position of the siphuncle. 
Fig. 4 c . A fragment of the smaller extremity of the shell, which 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. 
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