120 Trans. Acad. Sci. of St. Louis. 



obsolete in parts of the shell. The cross-section of this 

 species is circular rather than elliptical as in 0. 

 whitei, although the elliptical cross-section of the latter 

 species may be due to a slight compression of originally 

 cylindrical shells. It is said by Winchell that this species 

 tapers more rapidly than 0. ivhitei. This may be true in 

 general, but the two species overlap in this characteristic, the 

 type specimens of O. whilei varying from 5° to 8° and 0. 

 heterocinctus from 6° to 10°. The material representing both 

 these species, leaves much to be desired, it being for the 

 most part fragmentary, and the species can be properly 

 defined only when more perfect specimens are procured. 



Orthoceras indianense Hall. 



Pi. IX. f. 3. 



Several specimens of a small, smooth species of Orthoceras 

 with the sides tapering at an angle of about 8° with a circular 

 or slightly elliptical cross-section, and with a central or slightly 

 excentric siphuncle, have been observed in the Chonopectus 

 fauna. These were referred to the species O. indianense by 

 Winchell, and they seem to present no characters upon which 

 they can be separated from that species. The specimens are 

 all mere fragments, and more perfect material is needed to 

 certainly determine their essential characters. 



Phragmoceras expansum Win. 



PL IX. f. 2. 



Shell straight, rapidly expanding at an angle of about 70°, 

 very slightly constricted near the aperture. Transverse sec- 

 tion of the shell broadly elliptical, approaching circular. 

 Septa at distances of about 6 mm. Surface smooth in the 

 cast. The type specimen has a total length preserved of 

 about 35 mm., 21 ram. of which is included in the living 

 chamber; the longer diameter of the aperture is 52 mm. and 

 the shorter 45 mm., at the first septum the longer diameter 

 is 33 mm. and the shorter 27 mm. 



Remarks. The characters of this species are not very 

 definitely preserved. The specimen illustrated is the type, 



