Permo-Carhoniferous Ammonoids of the Glass Mountains 93 



on the umbilical shoulder; and the internal lobes consisting of a long 

 tongue-shaped, undivided dorsal or antisiphonal lobe and two pairs 

 of lateral lobes. There are, then, in all, ten external and five internal 

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

 than in Agathiceras. . . . The ontogeny of 5". Hyatti shows unmis- 

 takably that the genus is derived from Gastricoceras through Para- 

 legoceras, and is thus not a member of the Prolecanitidae. It may 

 possibly be an ancestor of the Arcestidae, but that question can be set- 

 tled only by a study of the ontogeny of the primitive Permian member 

 of this group." 



J. P. Smith united in this genus four species : Sch. fultonense Miller 

 and Gurley, Sch. Hildrethi Morton, Sch. Hyatti Smith, and Sch. mis- 

 souriense Miller and Faber, all from the Upper Coal Measures of 

 America. In his excellent study of Sch. Hyatti the author shows how 

 the suture of the genus develops from the Gastrioceran through the 

 Paralegoceran stage to that of Schistoceras, thus demonstrating that 

 this genus is the most complex member of the Glyphioceratidae . 



So far, Schistoceras only has been known from the Upper Coal 

 Measures (Uralian) where it does not seem to be very rare, especially 

 in the upper part (Cisco formation). In the western part of Texas 

 (Glass Mountains) we have found two new species, one in the Car- 

 boniferous and another one in strata perhaps about 1000 feet higher in 

 the lowest Permo-Carboniferous, our Wolfcamp formation. The first 

 of those species, Sch. Smithi nov. sp., occurs in shales with a rich fauna 

 of Pennsylvanian forms; it is relatively rare, one specimen having 

 been found by Dr. J. A. Udden, another one and a fragment by -Mr. 

 C. I.. Baker. The other species, Sch. diversecostatum n. sp., is very 

 frequent near Wolf Camp in the lowermost Permian, Mr. Baker and 

 the writer having been able to collect twenty- four specimens in a short 

 time. It occurs in a marly limestone and shales together with a rich 

 fauna of ammonoids, very few Gastropods, Pelecypods, Brachiopods 

 and a Trilobite. 



No Schistoceras has been found in any of the higher beds 



Schistoceras Smithi nov. sp. 

 PI. Ill, Fig. 9-16 

 Shell di'scoidal, involute, compressed laterally, with flanks flattened, 

 venter rounded. Cross-section parabolical, about as broad as high r 



