8o University of Texas Bulletin 



Noetling^ does not think that the trilobate form of the saddles is 

 of fundamental importance and tries to explain their origin simply 

 through the greater number of septa. He says that the points of the 

 lobes often reach to near the protuberance on the saddle of the next 

 following septum. This is certainly not the case in our species. The 

 points of the first lateral lobe touch only the upper part of the two 

 lateral saddles in the next septum, and in M. Whitneyi they do not even 

 touch those saddles. The trilobate form, therefore, cannot be ex- 

 l)lained simply by the crowding of the septa. I would rather suppose 

 that these different shapes of the saddles indicate different tribes or 

 sections of the genus. 



Our species can be easily distinguished from M. Whitneyi nov. sp., 

 by its deep adventive lobe A, and the position of Es2 ; there is also a 

 smaller nvmiber of rudimentary adventive lobes of the external saddle 

 in our species on specimens of the same size. In general, the saddles 

 in M. Burckhardti are higher and more slender than in M. Whitneyi. 



The other species found in Texas, M. Copei White^ belongs to an 

 entirely different group. Its saddles are tongue-shaped and not trilo- 

 bate, the form of the adventive lobe. A, is entirely different, and the 

 umbilical part of the external saddle, E,S2, is much lower. The suture 

 of M. Copei has a very great similarity to that of M. Orbignyana 

 Vern., although the external shape, especially the width of the venter 

 and the convexity of the flanks, is certainly different ; but the character 

 of the suture may prove to be more important in Medlicottia than the 

 external shape. M. Copei, by, the way, furnishes another proof that the 

 trilobate form of the saddles is not simply caused by the crowding of 

 the septa, because in this species the septa are very near each other, 

 and ^he saddles are simply tongue-shaped. 



Age: 



Word formation, Permo-Carboniferous. 



Number of specimens examined : 



About twenty. The species is very common in the lower limestone 



'NoeUing, Medlicottia und Episageceras, p. 358. 

 "White, The Texan Permian, p. 21, pi. 1, fig. 1-3. 



