202 palAMtoloot of new-tork. 



265. 18. ORTHOCERAS ANELLUM. 



Pl,. XLIII. Figs. 6 a, b, c, d, e,f. 

 Orthoeerat anellui. Coitkad, Proc. Acad. Nat. Sciences, 1843, Vol. i, p. 334. 



Elongated, very gradually tapering, annulated by prominent sharp slighlly sinuous 

 ridges which are distant about one fourth the diameter of the shell, longitudinally marked 

 by fine crowded wrinkled striae ; septa moderately convex ; siphuncle excentric, but not 

 marginal ; section circular. 



This species is readily distinguished from any of the preceding by the angular approxi- 

 mate annulations, which are sharper and more elevated than those of any other species 

 known in the rock. The length of the larger fragment figured is one inch and a half : the 

 diameter at the larger extremity is half on inch ; at the smaller end, three eighths of an 

 inch. The smaller specimen diflfers from the other in the striae being less crowded, though 

 otherwise similar. 



Fig. 6 a. A fragment of the septate portion of the shell, b. Transverse section of the same. 



Fig. 6 c. Enlarged portion, showing the strise, which, on a great part of the surface, are covered by a 



calcareous coating. 

 Fig. Q d. A smaller fragment, e. Transverse section. / Portion of the surface enlarged. 



Position and locality. The larger specimen is from Mineral Point ( Wisconsin) , where it 

 is associated with several other Trenton limestone species. The smaller specimen is from 

 the lower part of the same rock at Middleville. {Cabinet of Mr. Conrad.) 



266. 19. ORTHOCERAS UNDULOSTRIATUM ( 71. *p.). 



Pu XLIII. Figs. 7 a - A. 

 Compare 0. trochlearU, Hisingeh, Leth. Suecica, pag. 28, pl. 9, fig. 7. 



Cylindrical, very gradually tapering, annulated by oblique undulating angular ridges, 

 which are distant about one fourth the diameter ; annulations transverse on the ventral 

 side, and abruptly arching towards the apex on the dorsal side ; surface marked by fine 

 crowded transverse undulating striae ; section circular ; siphuncle slightly excentric. 



This species is readily distinguished from the others, by the transverse undulating striae 

 without longitudinal lines. The annulations are subangular, and abruptly arched on the 

 dorsal side, in this respect resembling the longitudinally striated species. In its external 

 characters, it corresponds with O. trocMearis of Hisinger ut supra ; but the position of the 

 siphuncle is more nearly central, and the annulations more angular. 



This species may be confounded with 0. bilineatum, and the variety of that speCies, 

 where the shell is removed ; but it differs from those, in the more angular character of the 



