544 PALEONTOLOGY OF ILLINOIS. 



thickness, or transverse diameter, about 1 inch; dorso-ven- 

 tral diameter of last turn, near the aperture, 0.86 inch. 



Among the specimens before us, there are two forms that may pos- 

 sibly belong to distinct species. One of these, which we consider the 

 typical form of the species here described, has the periphery very 

 depressed convex, while in the other it is distinctly more convex, or 

 rounded. As they agree, however, apparently almost exactly in all 

 other known characters, and both forms seem to vary somewhat in the 

 convexity of the periphery, we are inclined to view them as merely 

 varieties, or probably the different sexes of one species. In the more 

 convex form, the lateral nodes seem to be generally a little more inclined 

 to become slightly elongated in the direction of the transverse diameter 

 of the whorls, though this character appears not to be entirely constant. 

 In both forms the longitudinal, or revolving surface ridges and furrows, 

 become nearly or quite obsolete toward the aperture on the body whorl. 



Internal casts of this species seem to be almost exactly like speci- 

 mens figured by European authorities under the name N. tuberculatm, 

 Sowerby. As that species, however, attains a much larger size, and 

 has, according to Prof. McCoy's description, a very large siphuncle, 

 while none of the figures or descriptions of it we have seen either show or 

 mention the distinct longitudinal, or revolving costse, so \vell defined on 

 the surface of our shell, we can entertain no doubt in regard to its being 

 clearly distinct. It is true, the figures of N. tuberculatus alluded to all 

 .represent only internal casts, while the longitudinal markings seen on 

 our shell are not indicated on casts of its interior ; but it is scarcely pos- 

 sible that such markings should never have been observed, as impres- 

 sions in the matrix, if not otherwise, had they existed in N. tuberculatus. 



The specific name of this shell was given in honor of Prof. E. T. Cox, 

 the State Geologist of Indiana. 



Locality and position Waterloo, Illinois, and Greencastle, Indiana ; 

 from the St. Louis division of the Lower Carboniferous. 



NAUTILUS (SoLENOCHEiLTis) COLLECTUS, M. and W. 



PI. 23, Fig. 3 and 4. 

 Nautilus (Solenocheilus) cottectus, MEEK and WOKTHEX. Proceed. Acad. Nat. Sci., Phila., 1870, p. 48. 



SHELL thin, attaining a moderate size, slightly com- 

 pressed or subglobose in general form; umbilicus rather 

 small, but deep, perforated, and provided with very abrupt 

 walls, particularly near the aperture. Volutions about one 



