76 University of Texas Bulletin 



beds with M. Copei are probably a little older than those with M. 

 Whitneyi. 



Age: 



Leonard formation, Permo-Carboniferous. 



NiDiiber of specimens examined: 

 One. 



Locality: 



About two miles W N W from Iron Mountain, at the foot of an ex- 

 tensive clay slide. Glass Mountains. 



Pig. 2. Mature external suture of Medlicottia BurckJiardti nov. sp. 



Medlicottia Bnrckhardti nov. sp. 

 PI. I, Fig. 46-52; PI. II, fig. 1-3 



Shell discoidal, very involute, flattened on the flank, and with sharp 

 keel on both sides of the very narrow venter and deep median groove 

 between them. The cross-section is sagittate, slightly excavated and 

 truncated at the ventral portion and profoundly incised at the dorsal 

 side by the next smaller whorl. The flanks are not completely flat 

 but very slightly and evenly convex; keels on the venter are very 

 sharp in younger individuals. Their highest part is at the ventral 

 shoulder and from there the shell slopes in a slight curve down to the 

 border of the median groove. In the largest specimens the keels be- 

 come entirely rounded. The whorls are deeply embracing. The um- 

 bilicus is very small, the umbilical border is slightly rounded, and the 

 umbilical wall is narrow but steep. 



