412 REPORT ON THE STATE CABINET. 



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 diffei'ent 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 0. loxias, which has a very 

 similar external character. This character may be subject to some 

 variation. 



Formation and Localitij. — This species occurs in strata below the 

 Racine and Waukesha beds proper, and in the same horizon with 0. 

 annulatum.* 



Orthoceras medullare. Hall. 



PLATE XX, FIGS. 1, 2. 



Orthoceras medullare, Hall. Rep. Prog. GeoL Survejf Wisconsin for 1859, p. 4. Feb., 1860. 

 Orthoceras slricelineatuin, M'Chesney. New Palaeozoic Fossils, p. 94. Feb., 1861. 



Shell cylindrical, often a little compressed, gradually, and in some speci- 

 mens more rapidly tapering. The septa are distant nearly half the 

 diameter, but are subject to considerable variation in the same indi- 

 vidual, so that nearly three chambers are sometimes included in a 

 length equal to the diameter. The siphuncle is large and slightly 

 expanded between the septa. 



The surface is marked by strong, sharp, subequal longitudinal strise, 

 which are cancellated by fine transverse striae. The longitudinal striae 

 are often alternated by finer sharp striae in the same direction. Surface 

 of the cast smooth, and by this character it is distinguished from the 

 casts of 0. columnare and 0. angulatum. 



Formation and Locality. — In limestone of the Niagara group, at Wau- 

 kesha and Wauwatosa, Wisconsin. 



* The Orthoceras scammoni, M'Chesnet, New Paloeozoic Fossils, is probably identical with 

 this species. Two specimens received from Prof. Maect offer some elucidation of the characters 

 of the fossils not before understood. A single specimen combines in itself characters of O. 

 colunvnare and 0. scammoni ; and unless we can find suflBcient differences, on a further examina- 

 tion of collections, to sustain the separation, the O. scammoni and others, as well as that referred 

 by me to O. angulatum, will fall under O. columnare, which has pr.ority in time over those 

 described by M'Chesnet. The cancellated figs. 10 and 11, of Plate xix, are apparently only the 

 well preserved impressions of the external surface markings of the same species. It is probably 

 also the same species which has been described bj^ Mr. Billings, in 1866, as Orthoceras cadmus. 



