Permo-Carhoniferous Ammonoids of the Glass Mountains 95 



The dimensions refer to the largest specimen found ; the second one 

 is only slightly smaller, but a little crushed. The ratio of dimensions 

 seems to be the same. Both specimens are septate throughout so that 

 the original size must have been much larger. 



Relation to other species : 



All the species of Schistoceras so far described are very similar to 

 each other. This circumstance cannot surprise us much, because the 

 only difference could be in the ratio of dimensions and perhaps slight 

 details of the suture. 



Our species is very similar to Sch. Hyatti Smith^, the type species 

 of the genus, but it has a different cross-section, the flanks of our 

 species being more decidedly flattened, while those of the type species 

 are rather rounded (Smith, pi. 20, fig. 8). The ratio of dimensions is 

 not very different, being in our species 1:0.48:0.51:0.17:0.19 and in 

 Sch. Hyatti, 1:0.51:0.51:0.17:0.20. There are slight differences in 

 the suture. The median saddle of the siphonal lobe is comparatively 

 higher in our species. The saddles are stouter and not constricted, the 

 branches of the siphonal lobe are more asymmetrical, the shape of the 

 second lateral saddle is very different, the greater part of the auxiliary 

 saddle is on the flank, etc. 



From all the other species so far described our species apparently 

 differs still more, especially by the greater height of the whorls. 



There is no very great difference between the species described 

 here and Sch. diver sec ostatum from the Permo-Carboniferous. This 

 latter one has more rounded flanks and a wider umbilicus ; the sutures 

 resemble each other very much, but that of Sch. Smithi seems to have 

 stouter saddles. 



Age: 



Gaptank formation, Pennsylvanian (Uralian). 



Number of specimens examined: 



Three. The species is rare at the locality. 



Locality: 



Al:ni:t 2 miles south of Gap Tank, Glass Mountains. 



"J. p. Smith, Oarb. Amm. of North America, p. 108, pi. 20, fig. 1-8; pi. 21, fig. 10-13. 



