Permo-Carhoniferous Ammonoids of the Glass Mountains 71 



Certainly it is much deeper in M. primas than in any of the other 

 species described, but I cannot see any essential difference in the ad- 

 ventive lobes of M. Orbignyana and M. Verneuili. If the depth of 

 the adventive lobe really had some relation to the age of the species, 

 then M. Verneuili would have to be considered as much younger than 

 M. Marcoui, M. bifrons and M. Trautscholdi. Karpinsky himself 

 remarked that the whole difference between M. Orbignyana and M. 

 Trautscholdi may be only one of size, and justly indicates that the 

 suture of the small specimen of M. Orbignyana figured in his pi. 2, 

 fig. I, g, h, k, is extremely similar to that of M. Trautscholdi. Noetling 

 recognizes this fact but thinks that Karpinsky overlooks the smaller 

 number of adventive lobes (Noetling, loc. cit., p. 362); but, I must 

 say that I am unable to see any such difference between the suture in 

 pi. 2, fig. I k, of Karpinsky, and pi. 8, fig. 31, of Gemmellaro. The 

 number of these rudimentary adventive lobes simply increases with 

 the size of the animal. 



Noetling thinks also that in the geologically older species the lateral 

 lobes, with exception of the first one, have a longer finger on the um- 

 bilcal side than on the side nearer to the venter. But he himself re- 

 marks that this can only be seen in M. Marcoui and M. Trautscholdi. 

 This observation, made by Noetling himself, shows at once tl*at this 

 character cannot be of any importance at all, because all the Sicilian 

 species come from the' same bed, the "Calcare compatto" ! 



I think that Noetling's assertion that the depth of the adventive 

 lobe and the number of rudimentary adventive lobes or the -relative 

 length of the branches of the lateral lobes can be used to determine the 

 geological age of a species, cannot be sustained. These characteristics 

 depend mostly upon the size of the individual or are altogether in- 

 significant. 



Tchernow's proposition to divide Medlicottia into two groups, one 

 with two keels or an angular ventral side, and another with a ventral 

 part limited by rows of tubercles, cannot very well be accepted. This 

 would again place M. artiensis in the genus Medlicottia from which 

 it certainly should be separated. On the other hand the principle could 

 not be applied to our M. Whitneyi, which on the inner whorls shows 

 a row of tubercles on both sides of the median groove, while it has 

 sharp keels on the outer whorl (pi. I, fig. 42, 43, 45, 45a). 



