200 University of Texas Bulletin 



shallowing- of the lobes beginning- with the second auxiliary lobe. The 

 character of the saddle is also very similar, especially the tongue-like 

 shape with the lateral swellings at different heights. We can distin- 

 guish our species from the Russian one only by minor details, as the 

 greater width of Esi in M. Orhignyana, the somewhat narrower lat- 

 eral and auxiliary saddles, the higher secondary saddles which divide 

 the lobes, the narrower venter, etc., in our species; but the general 

 form and the character of the suture are certainly surprisingly similar. 

 Thus we find in the lower Permo-carboniferous of Central Texas 

 another form which is intimately related to a species from the Artinsk, 

 and we may say that this latter formation corresponds to at least two 

 different formations or horizons of our region, (the Wichita at least 

 in part) and the Clear Fork formations. 



If we compare now the different forms of Medlicottia which have 

 been found in Central Texas, we see that they probably constitute only 

 different stages of development in a single tribe. The relationship 

 between the Medlicottia from Runnels County and M. Copei is quite 

 evident. There is scarcely a doubt that the one developed from the 

 other, although this has to be proven later on when the development 

 of the lobes in both species can be studied. But there is even a pos- 

 sibility that the older form of Medlicottia collected by Wrather at 

 four miles south from' Dundee in Baylor County, also may be ante- 

 cessor of the later ones. If we compare the development of the sut- 

 ure in M. Orhignyana Vern., we see that at the stage where the Medli- 

 cottia suture develops from the Sicanites stage (compare fig. le and 

 ij, in Karpinsky's work), which corresponds to a height of the whorl 

 of not quite seven millimeters, this suture is surprisingly similar to 

 that of our Medlicottia from four miles south of Dundee. In this 

 stage the keels are also strongly beaded, while later on they become 

 sharp. This circumstance allows us to conclude that there may possi- 

 bly be a similar development in our own species and that the three 

 different forms of Medlicottia discussed here may belong to the same 

 tribe and constitute simply different stages of development. We do 

 not know yet in what relationship M. artiensis and M. Orhignyana 

 stand, and if they are found always at the same horizon, but even 

 if this were the case, we should not be surprised as it is very possi- 

 ble that only part of the tribe developed a more differentiated suture, 



