ICO Cephalopoda of the Cincinnati Group. 



Orthoceras Ortoni — (Meek, 1872). 



■Shell rather rapidly expanding, from the posterior toward the 

 •aperture ; section oval, or more or less nearly circular ; septa rather 

 closely arranged ; siphuncle lateral, being at one of the narrow ends of 

 the compressed section, but not quite marginal, of comparatively 

 moderate size, and apparently beaded; surface of cast showing traces 

 of regular, obscure, longitudinal ridges, that were probably not defined 

 on the exterior of the shell, which is unknown. 



A compressed specimen, 2.30 inches in length, measures at the large 

 end 1.37 inches in breadth one way, and 0.44 inch the other, while, 

 at the smaller end, its greater diameter is 0.38 inch, and its smaller 

 0.24 inch. The septa at the large end are separated 0.15 inch, and at 

 the smaller end 0.07 inch. 



Prof. Meek expresses a doubt as to wliether or not this species be- 

 longs to the genus Cyrtnceras. 



Found at Cincinnati ; range unknown. 



Genus Endoceras — (Hall, 1847). 



[Etym. — Endos, within; and keras, horn.] 



Shell straight, conical ; siphunele large, usually excentric, smooth, 

 except as marked on the outside by the septa. Within the siphunele 

 are one or more very elongated conical tubes, often one within another, 

 to the number of four or five. 



Endoceras proteiforme — (Hall, 1847). 



General form cylindrico-conical, more or less elongated, often coin- 

 j^ressed, tapering somewhat unequally in different specimens; young 

 specimens terminating in an extremely acute point; surface marked 

 hy distinct transverse strise, which usually appear like narrow subim- 

 bricating bands, with one edge well defined and more elevated than 

 the other, more or less distinctly striated longitudinally ; striae varying 

 from extreme tenuity to distinct elevated thread-like lines ; section 

 circular ; septa distant from one fifth to one fourth the diameter ; 

 siphunele excentric or submarginal. 



Its range seems to be co-extensive with the Cincinnati Group, 

 but anything approaching a good specimen is quite rare. 



