FOSSILS OF THE NIAGARA GROUP. 413 



Orthoceras angulatum, Wahl. 



PLATE XIX, FIGS. 10, 11 ; PLATE XXIV, FIG. 1. 



Orthoceras angidatwn, Wahlenbeeg. Nova Acta Soc. Sci. Upsal, p. 90. 1827. 

 Orthoceras angulatum, Hisinger. Lethea Sueoica, p. 28, Tab. x, fig. 1. 

 Orthoceras virgatum, Sowerbt; in Murciiison's Silurian System, p. 622, Tab. ix, fig. 4. 

 Orthoceras virgatum? Hall. Palajontology N. Y., II, p. 291, Plate Isiii, fig.s. 2, 3. 

 Compare O. canaliculaium, Sowerbt ; in Murchison's Silurian System, p. 632, Tab. xiii, fig. 26. 



Specimens from Wisconsin are apparently identical with those of New 

 York referred as above ; the former being casts of the interior, while the 

 latter are preserved in a soft calcareous shale, and have the sm-face 

 markings more or less obscured. 



The septa are distant about one-fourth the diameter of the shell. The 

 siphuncle is central or subcentral, with scarcely an apparent expansion 

 between the septa. 



The longitudinal ridges are angular, and about one line distant when 

 the shell is an inch in diameter. The finer surface striae are but imper- 

 fectly preserved on the cast, and it is only in the impressions of the 

 exterior that these markings become conspicuous. 



This is probably the species described by Mr. M'Chesney, in a paper 

 published in 1861, under the names 0. scammoni, 0. hop, 0. lineolatmn, 0. 

 hregulare = 0. woodworthi. The last one figured in a fragment less than an 

 inch in length. A gutta-percha cast sent by Prof. Winghell under the 

 name 0. scammoni, corresponds very well with specimens referred by me 

 to 0. angulatum. Should the species prove distinct from the European 

 one, we may select a name from among those above cited. The com- 

 parison of a considerable collection of specimens from Bridgeport and 

 the various localities in Wisconsin has not convinced me that we have 

 so large a number of species of a character so similar as those above 

 cited. 



Formation and Locality. — In limestone of the age of the Niagara group, 

 at Racine, Wisconsin, and Bridgeport, Illinois. 



Orthoceras crebescens, n. s. 



PLATE XIX, FIGS. 1, 2, 3. 



Shell large, rapidly tapering ; transverse section circular ; septa deeply 

 concave, four and a half of the intervals being equal to the diameter 

 of the shell. Siphuncle moderately large, central or subcentral. 



