106 CARBONIFEROUS AMMONOIDS OF AMERICA. 



five internal lobes, four more than are possessed by Paralegoceras, and two 

 more than Agatliieeras. 



Professor Hvatt has kindly turned over to the writer the type specimen 

 of Schistoceras, and through the kindness of Dr. Stuart Weller the type of 

 Schistoceras {Gon.) fultonense Miller and Gurley was open to his inspection. 

 Haug has also refigured Schistoceras hildrethi Morton, so that all the known 

 species of this genus were available for study. The type species has never 

 been named until now, but the laws of priority demand a recognition of 

 Hyatt's genus. 



The ontogeny of 6'. //^rt//!i shows unmistakably that the genus is derived 

 from (iastrioceras throuofh Paraleaoceras, and is thus not a member of the 

 Prolecanitidffi. It niay possibl}' be an ancestor of the Arcestidse, but tliat 

 question can be settled only by a study of the ontogeny of the primitive 

 Permian members of this group. 



Occutrence. — At i)resent the genus Schistoceras is known only from 

 America, in the Upper Coal Measures. 



Schistoceras ful tonense Miller and Gurley. 

 PI. XVI, figs. 15-17. 



1890. Goniiitif's fultonensis, Miller and Gurley. Bull. Illinois State Mus. Nat. Hist. 

 No. 11, p. 39, Fl. IV, tigs. 15-17. 



The following description is quoted from Miller and Gurley's paper: 



Species medium size, subglobose, periphery regularly rounded : volutions rather 

 rapidly expanding. Transverse section of a volution semiellijjtical, the transverse 

 diameter being a little more than the dorso-ventral. Number of volutions not known. 

 The last volution embraces all the inner ones. Umbilicus small, open but not disclos- 

 ing the inner volutions. The sides of the volutions are slightly flattened and inclined 

 toward the regularly rounded peripherj'. The sides of the umbilicus are abrupt, and 

 the greatest transverse diameter of a volution is near the abrupt descent to the 

 umbilical cavity. The external shell of our specimen is not preserved. 



The septa are lanceolate, the saddles all rounded and tongue-shaped, 

 the lol^es all pointed and slightly constricted at the middle. The external 

 lobe is long, rather broad, and divided by a siphonal saddle of equal 

 breadth. The superior lateral lobe is of equal length and similar to the 

 external; the second lateral lobe is aijout two-thirds of the length of the 

 superior lateral; the third lateral lobe is very small and stands well above 

 the umbilical shoulder; on the umbilical border is a foui'th lobe similar to 



) 



