138 University of Texas Bulletin 



Dimensions: 



I 11 



Diameter 24.0 mm (1) 20.0 mm 



Width 14.8 mm 0.60 ?11.5 mm 



Height of last whorl 11.9 mm 0.49 ?7.8 mm 



Diameter ot umbilicus... 2.8 mm 0.12 ?2.0 mm 



Relation to other species: 



Marathonites J. P. Smithi is very nearly related to M. sulcatus n. sp. 

 but the latter one is still more involute, its umbilicus is much narrower, 

 and its septa are much nearer together so that they almost touch each 

 other ; also the form of the lobes is different. In M. Smithi the central 

 one of the three points of the lateral lobes is much longer than the 

 others, while in M. sulcatus the three points are of nearly equal length ; 

 saddles and lobes are generally broader in the latter species than in the 

 former one. M. sulcatus has apparently four constrictions to the whorl 

 and these are much deeper than in M. Smithi. 



From M. vidriensis n. sp. our species is easily distinguished by the 

 broad interstices between the transversal striae, by the much more in- 

 volute form and narrower umbilicus and by the different internal 

 suture. M. Hargisi n. sp. has an absolutely different suture and may 

 even belong to a different subgenus. 



From Stacheoceras Ganti Smith our species is easily distinguished 

 by its wider umbilicus and the less numerous and straighter constric- 

 tions, also by higher saddles. St. Parkeri has an entirely different 

 suture. 



Very similar to our species seems to be Stacheoceras Romanowskyi 

 Karpinsky,-^ at least in the character of the septa, but it shows only 

 three lateral and auxihary lobes, while our species has four (five). 



A certain resemblance has also St. pygmaeum Gemm.^ at least in 

 the form of the lobes ; but there are only three of them as against four 

 in our species, and the branches of the siphonal lobe are simple instead 

 of bifid. 



Age: 



The species has been found only in the Wolfcamp division, the lower- 

 most part of the Permo-Carboniferous. 



'Karpinsky, Ammoneen d. Artinsk-Stufe, p. 77, pi. V, fig. 6, a-b. 



''Gemmellaro, Calc. c. Fusulina, p. 39, pi. 8, fig. 15-17. • 



