Permo-Carhoniferous Ammonoids of the Glass Mountains 83 



it may be best to let the question rest as it is until some author can 

 review all the paleozoic forms which belong to these groups. 



Tchernow evidently thought that something would be gained by 

 further subdividing Gastrioceras and thus he united the species from 

 the Artinsk under the name of Paragastrioceras. I have not been able 

 to find if the author ever gave a definition of this new genus and the 

 new species he considered as belonging to it. 



If theve is to be a subdivision of Gastrioceras, there should certainly 

 be established at least a subgenus for the group of G. Zitteli Gemmel- 

 laro^ ; that is to say, relatively evolute forms with strong transversal 

 rilxs at the umbilical shoulder, and strong spiral ribs on the ventral 

 portion and often also on the flanks, the transverse ribs often disap- 

 pearing in the outer whorls. This group is very well characterized, 

 seems to exist only in the Permian, and has a very wide distribution. 



Our material is not rich enough to allow us a subdivision of the 

 genus, but we shall see that two very different groups are represented : 

 one without strong transversal and spiral ribs, but with delicate trans- 

 versal and spiral lines in our lowermost beds, and another one repre- 

 sented by several species and clearly belonging to the group of Gastrio- 

 ceras Zitteli. 



Group of Gastrioceras globulosum M. a. W. 



Gastrioceras modestum n. sp. 



PI. II, Fig. 4-27 



Shell discoidal, composed of a great number of not very deeply em- 

 bracing whorls, moderately evolute, flanks and ventral portion broadly 

 rounded. Cross-section nearly semilunar. The umbilical shoulder is 

 very sharp, especially in the younger individuals, a little more rounded 

 but well-marked in the older ones ; the umbilical wall is slightly convex 

 and verv broad, and the umbilicus is moderately wide. The whorls are 

 much wider than high ; the greatest width lies at the umbilical shoulder ; 

 from there the shell suddenly bends down, forming a rather sharp 

 edge ; the umbilical shoulder, flanks and ventral portion form a single 

 curve, and cannot be distinguished from each other. Each whorl 

 shows three not very deep constrictions; these begin at the umbilical 



'Gemmellaro. Calc. c. Fusulina, p. 85, pi. 6, fig. 18-23; pi. 7, fig. 14. 



