GENUS ORTHOCERAS. 351 



GENUS ORTHOCERAS (Breyn). 

 ORTHOCERAS ANNULATUM. 



Orthoceras annulatum : Sowerbt, M. C. Tab. 133, 1818. 



Orthoceratites undulatus : Hisinger, Anteckn. V. Tab. IV, f. 6. Vet. Akad. Hand- 



lingar, Table vii, f. 8. 



" ' Lethea Suecica, p. 28, Tab. X,f. 2. 1827. 



Orthoceras annulatum : Murchison, Silurian system and Siluria. 



Orthoceras undulatum : Pal. New-York, Vol. ii, pa. 293, pi. lxiv and lxv. 



This species is of common occurrence in the shales of the Niagara group 

 in New- York. It is found in the lower beds exposed at Waukesha and near 

 Wauwatosa in Wisconsin. The specimens are casts, usually preserving 

 only the marks of the strong annulations, which vary considerably in their 

 sharpness and degree of elevation ; but there is no evidence of specific dis- 

 tinction among the forms of this character. The fine undulating transverse 

 striae are preserved in the impressions of the exterior surface, associated 

 with the casts. 



ORTHOCERAS COLUMNARE. 3S Q, OVtU 



Orthoceras columnare : Hall, Report of Progress Geol. Survey of "Wisconsin, 1859 



(Feb. 1860). 



Compare 0. canaliculatum : Sowerby, Sil. System, T. 13, f. 26. 



The species described by me from Wisconsin is elongate cylindrical, 

 very gradually tapering. The siphuncle is central, of medium size, and not 

 expanded betw:een the septa. The septa are distant about one half the 

 diameter. 



The surface is longitudinally fluted by low ridges which are about one- 

 sixth of an inch distant from each other. This feature is of course variable 

 upon specimens of different size. The intermediate striae are not preserved 

 in the casts, in which condition the species is usually found. 



In the typical specimens, the septa are very distant, and in this respect 

 it is conspicuously different from the following species. This character may 

 be subject to some variation. 



This species occurs in strata below the Racine and Waukesha beds 

 proper, and in the same horizon with O. annulatum. 



47 



