126 CARBONIFEROUS AMMONOIDS OF AMERICA. 



The specific name is given in lionor ot' Dr. Stuart Weller, of the Uni- 

 versity of Chicago. 



The tvpe is figured on PI. XXI, figs. 1 and 2. It was presented to 

 the writer by Dr. Gant, and was collected from the Cisco formation, Upper 

 Coal Pleasures, of Graham, Tex. It is in the writer's collection in the 

 Leland Stanford Junior University, California. 



Genus DiMOKPHOcERAS Hyatt. 



The type of this genus " was Goniatites r/ilhertsoni Phillips. All the 

 species are rather compressed, involute, smooth shells, with narrow 

 umbilicus. The surface is ornamented only by the curved cross strias of 

 growth. The ventral lobe is divided by a deep, notched, siphonal saddle, 

 and the two lobes thus formed are divided a second time, giving a pair of 

 short, narrow ventral lobes on each side of the abdomen. On the middle 

 of the flank there is a deeper, pointed lateral lobe, and another on the 

 umbilical shoulder. Inside, concealed by the involution, is a tongue- 

 shaped antisiphonal lobe, flanked on each side by a pointed lateral. Thus 

 there are three internal lobes, six external, and a pair on the umbilical 

 shoulders, eleven in all. lliis is the same number as in Paralegoceras, 

 but of different character. In Fdralegoceras the multiplication of lobes 

 takes place within the umbilical border, but in Dimorplwceras the internal 

 luiraber is normal and the extra pair of lobes is formed by division of 

 the ventral lobes. This genus probably comes from Goniolohoceras, by 

 secondary division of the external lobes. 



Occurrence. — Dimorphoceras occurs in Europe in the Lower Carbonif- 

 erous and the Coal Measures ; in America it is known only from the 

 Upper Coal Measures, Cisco formation, near Graham, Young County, 

 Tex., the specimen described in this paper being the only one known to be 

 in any collection. 



Dimorphoceras texanum Smith, sp. nov. 



PI. XX, figs. 12-15. 



Shell discoidal, compressed, involute, with narrow umbilicus, flattened 

 sides, and greatest breadth at the umbilical shoulders. Venter narrow, 

 flattened, angular, and slightly fuiTOwed at niaturity, but rounded in 



('A. Hyatt, Proc. Boston Soc. Nat. Hist., Vol. XXH, p. 331. 



