CEPHALOPODA. 457 



This species is distinguished among others here described, by its wide 

 umbilicus and gradually enlarging volutions, and in its flattened condition, 

 by the fine, even, thread-like strise. The species was originally founded 

 upon specimens like figures 10 and 11 of plate 70, in which the septate char- 

 acter is usually very obscure, and often not all preserved, the general form 

 and surface-markings being all that remain. The specimen figure 8, plate 70, 

 is a cast of the interior, from which all remains of the external shell have been 

 removed. The volutions are somewhat rotund. 



The form described as Clymenia Erato=Goniatites Erato is probably only 

 a variety of G. complanatus. The specimens are larger than G. complanatus 

 in its usual condition, and the outer volution embraces somewhat more of 

 the inner one ; but with these exceptions they are too nearly similar to be 

 separated, especially as no complete comparison can be made between the septa 

 in the two forms. 



Among a considerable number of specimens, preserving the general form and 

 proportions of figures 10 and 11, of plate 70, but little difference has been 

 observed. The specimen figure *12 of plate 71 has a much greater diameter, 

 and the proportional distance of the septa is greater than in any previously 

 recognized form of G. complanatus. It is readily distinguished from G. sinuosus 

 by the direction of the septa, though the general form of the shell and surface- 

 markings are similar. 



Formations and localities. In the green shales of the Portage group, at Cash- 

 aqua creek, in Livingston county, N. Y.; in the lower beds of the same forma- 

 tion, on the east side of Cayuga lake ; and in some concretionary layers in the 

 upper part of the Hamilton group, on the shore of Lake Erie. 



58 



