200 PALJEONTOLOGT OF NEW-YORK. 



than in the last species, but still rounded. Tlie transverse fine striae, under the magnifier, 

 give a kind of varicose appearance, being closely arranged and slightly arched between 

 the longitudinal ones, following the oblique direction of the annulations. The difference 

 in the size of the longitudinal and transverse lines is a striking peculiarity of the species, 

 rendering it readily distinguishable from the last. 



I have referred above to the O. calamiteum of Munster, which, however, is from the 

 higher silurian or devonian rocks, from which circumstance alone it is proper to presume it 

 distinct from this one. The figure of Portlock corresponds in some degree with our species, 

 but is represented with two or three finer longitudinal striae between the larger ones, while 

 the transverse striae are as strong as the fine longit\idinal ones ; in which characters, the 

 one under consideration is quite different. M. de Vernedil has represented the O.calamiteus 

 as destitute of transverse striae ; though the one referred to that species by D'Archiac and 

 DE Verneuil, cited above, has transverse striae. 



The species under consideration js not only quite distinct from 0. tubidnella of Sowerby, 

 but from all the species in our higher strata, though having some resemblance to them. 



Fig. 2 a, J. View of two individuals, showing the annulatioDS and longitudinal striae. 



Fig. 2 c. Transverse section of b. 



Fig. 2 d. Portion of the surface enlarged. 



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

 Turin and Lowville. A fragment or impression of the same species has been found at an 

 exposure of the Trenton limestone one mile eeist of Albany, which was incorrectly figured 

 on Plate VII. (See page 35). (State Collection.) 



262. 15. ORTHOCERAS BILINEATUM, var. a. 



Pl. Xmi. Figs. 3 a, b, c, d. 



This variety differs from the typical forms, in the absence of the intermediate finer 

 longitudinal striae ; the single series, which is pretty constant, corresponds in distance to the 

 coarser ones in the other specimeqs. A careful examination of several specimens, however, 

 has shown an occasional deviation from this rule, and smaller striae are sometimes present. 

 In other characters, it is not essentially different from the last, and therefore can scarcely 

 constitute a distinct species. 



Fig. 3 a. A fragment of this variety. 



Fig. 3 b. Transverse section, slightly compressed, showing the siphon. 

 Fig. 3 e. An enlarged portion of the surface. 



Fig. 3 ^. A fragment denuded of the shell, showing the lines of septa which do not correspond to the 

 annulations. 



Position and locality. Same with the preceding. 



