324 PALEONTOLOGY OF ILLINOIS. 



ORTHOCERAS OKAWENSIS, Sp. nov. 



Shell elongate, slender, very gradually tapering to the apex ; septa 

 concave, about 4 of them usually in the space of one diameter, 

 Siphuncle subcentral, surface markings unknown. 



This shell has a general resemblance to 0. Riishensis of the Upper 

 Coal Measures, but differs from that in the position of the siphun- 

 cle, which in our species is decidedly subcentral. 



Position and locality : Chester limestone, vicinity of the Okaw 

 bluffs, near Eed Bud, Eandolph county, Illinois. 



No. 2,485, of the Illinois State collection. 



ORTHOCERAS LASALLENSIS, Sp. nov. 



Shell small, gradually tapering. Surface ornamented with trans- 

 verse ridges or elevations; situated at irregular distances from each 

 other, and with delicate thread-like striae which cover the transverse 

 ridges as well as the spaces between them. The ridges and striae 

 will serve to distinguish this species from any hitherto found in the 

 Coal Measures, its ornamentation resembling that of the 0. undu- 

 latum of the Niagara limestone more closely than any other known 

 American species. The fragment preserved seems to belong to the 

 non-septate portion of the shell. 



Position and locality: Eoof of the middle coal, LaSalle, 111. 



No. 2,486, of the Illinois State collection. 



PLEUROTOMARIA MONTEZUMA, Sp. nov. 



This fine shell is only known from an imperfect cast of the last 

 whorl, which may be described as follows : 



Shell attaining a large size, broadly conical in outline; whorls 

 three or more, rapidly diminishing in size towards the apex. Last 

 whorl obliquely flattened, showing a surface about two inches 

 in breadth, which is traversed by about eight rather strong revolv- 

 ing striae, separated by shallow depressions that are about f of an 

 inch wide near the aperture. The under side of this whorl was also 

 traversed by numerous revolving stria3, about half as far apart as 

 those on the upper side, but their number can not be fully deter- 

 mined by the specimen in hand. A raised line around the inner 

 side of the whorl indicates the presence of a rather wide and deep 

 umbilicus. 



