Permo-Carboniferous Ammonoids of the Glass Mountains 99 



with a diameter of 10.5 mm. it is i :o.38, and in a still smaller one with 

 a diameter of 7.7^ mm. it is i :o..s.S, while in our smallest specimen 

 with a diameter of 4.2 mm. it is i :o.26. A similar difference can 

 be shown to exist in the ratio of width and height of the last whorl; in 

 general the height of the whorls is always comparatively greater than 

 in similar specimens of Sch. Hyatti. A great difference exists between 

 the two species with regard to the internal suture, the first lateral lobe 

 being much longer than the antisiphonal lobe in our species, while in 

 Sch. Hyatti it is much shorter. 



The other species of Schistoceras so far described seem to be much 

 more different yet, although some of them are still imperfectly known. 



Age: 



Wolfcamp formation, lowest Permo-Carboniferous. The present 

 species is of certain interest insofar as it represents the first Schis- 

 toceras found in the Permo-Carboniferous. 



Number of specimens examined: 



Twenty-five. The species is rather common at the only locality 

 where it has been found. 



Locality: 



Immediately northwest of Wolf Camp, Glass Mountains. 



Paralegoceras Hyatt 



Hyatt established this genus for forms similar to Gastrioceras, but 

 with higher arched whorls, narrower umbilicus and less prominent 

 ornamentation, but with sutures similar to Gastrioceras. 



Karpinsky later on has shown that the suture line offers a possi- 

 bility of distinguishing both genera, Paralegoceras having ten lobes 

 against eight of Gastrioceras, counting the two branches of the si- 

 phonal lobe as a single lobe. The pair of lobes which Paralegoceras has 

 in excess of Gastrioceras is the second lateral one, which is visible on 

 the flank, while in Gastrioceras only one lateral lobe is visible on the 

 flank. Thus those forms which show two lateral lobes on the flank 

 should be considered as belonging to Paralegoceras. But sometimes, 

 in Gastrioceras, the auxiliary lobe which generally lies on the umbilical 



