Permo-Carboniferous Ammonoids of the Glass Mountains 85 



Relation to other species: 



The present species is not a very characteristic one. It is somewhat 

 similar to Gastrioceras subcavum Miller and Gurley^ but has a nar- 

 rower umbilicus, and the umbilical shoulders are a little more rounded. 



Another species which resembles ours is Gastrioceras sitbglobulosum 

 Meek and Worthen^ but its umbilical shoulders are a little more 

 rounded, the umbilicus is narrower and the ventral region is much 

 flatter. . 



Both species have been found in the Cisco formation; it is thus not 

 very surprising that related species should occur in the next higher 

 zone, the base of the Permo-Carboniferous. But in general it is not 

 possible to give much importance to this kind of simple forms which 

 show no characteristic ornamentation and which present a suture line 

 that is general in practically all the species of the genus from the Car- 

 boniferous to the Permian. 



Age: 



Wolfcamp formation, Permo-Carboniferous. 



Number of specimens examined : 



Thirteen. The species is quite frequent at the locality. 



Locality : 



Immediately northwest of Wolf Camp, Glass Mountains. 



Group of Gastrioceras Zitteli Gemm. 

 Gastrioceras roadense nov. sp. 

 PI. II, Fig. 28-47 

 Shell discoidal, evolute, compressed on the flanks, ventral portion 

 rounded in the adult specimens. In the adolescent stages the flanks are 

 less flattened and the ventral portion more rounded; in the young 

 specimens the flanks and ventral portion are evenly curved. The um- 

 bilicus is moderately large, forming a very sharp umbilical shoulder 

 in the adult specimens (pi. II, fig. 41), while in the adolescent and 

 young ones (pi. II, fig. 28-41) it is more rounded. The umbilical wall 



^J. p. Smith, Carb. Amm. of America, p. 97, pi. 17, fig. 15-17. 



'J. P. Smith, Carb. Amm. of America, p. 89, pi. 6, fig. 1; pi. 21, fig. 7-9. 



