1 86 University of Texas Bulletin 



Still naich more similar to our species is the suture of the juvenile 

 specimens of M. Orbignyana with a diameter of about lo mm. For 

 example, the suture reproduced by Karpinsky (loc. cit. pi. 2, fig. i-j) 

 can scarcely be distinguished from that of Medlicottia n. sp., the only 

 real difference being that the Russian form has two auxiliary saddles 

 less than ours. But the shape of Esi is practically the same, as well as 

 the form of the lobes and saddles on the flank. We note that in the 

 Russian juvenile form the branch Esi also shows only one rudimentary 

 adventive lobe on the siphonal side aind two on the umbilical side, the 

 higher one being developed only as an insignificant notch, while in 

 ours it is very little deeper. The adventive lobe A is not yet divided by 

 a secondary saddle in the Russian form, which saddle develops in a 

 later stage (pi. 2, fig. I-k), while in ours it is very distinct. Another 

 difference is the greater depth of the siphonal sinus in the Russian 

 form, but this character changes quickly and in pi. 2, fig. I-k we note 

 a siphonal sinus similar to the one in our species. 



Considering the similarity of this juvenile form of M. Orbignyana 

 we are probably justified in concluding that our species represents a 

 form somewhat older than the Russian species, because it evidently 

 possesses a suture which in the latter one is only found in the internal 

 whorls where these develop from the Sicanites stage. 



Our new Medlicottia can be considered as the first American form 

 found that is distinctly related to a species of the Russian Artinsk. 

 This confirms our opinion expressed in the first part of this paper, 

 that at least a part of the cephalopod-bearing sandstone of the Artinsk 

 is represented in America by part of the Wichita formation. Another 

 part may be represented by the Clear Fork formation, as we shall see 

 farther on. 



Our Medlicottia is entirely different from M. Copei White, which 

 has been found in the same county and, according to Wrather, at a 

 little younger horizon. The branch Esi, of the external saddle, is much 

 higher and more complicated in the species described by White, the 

 number of the auxiliary lobes is greater, the keels are apparently less 

 beaded,^ and the cross-section is quite different. Still there are some 

 features in both species which show that the younger one may have 



»J. p. Smith, Carb. Amm., p. 48, says that the keels of M. Copei are slightly beaded 

 while White does not mention this characteristic at all. 



