Permo-Carboniferous Ammonoids of the Glass Mountains 167 



dentations. The first and second lateral saddles are practically built on 

 the same plan as the external one. They also end in a phylloid point 

 but the next lower pair of secondary saddles branches ofT from the 

 same place. The lateral saddles are lower than the external one. The 

 three auxiliary saddles are more or less similar to the lateral one, 

 but have a smaller number of branches. The third auxiliary saddle 

 lies on the umbilical seam, the second one on the umbilical shoulder. 

 The internal suture is unknown in this species. 



Dimensions : 



Diameter 39.8 mm (1) 



Width 20.4 0.51 



Height of last whorl 18.5 0.46 



Diameter of umbilicus 7.0 0.18 



Relation to other species: 



At first glance, our species is very similar to Perrinites vidriensis, 

 but it is easily distinguished by its different involution and the deeper 

 embracing whorls. When we compare the ratio of dimensions of P. 

 compressus with the nearest one in size (No. VII of the table of di- 

 mensions) of P. vidriensis, we find that they are very different, the 

 ratio being in the present species 1:0.51:0.46:0.18, and in the other 

 one I :o.57:o.52 :o.ii. We may still add that the flanks of our species 

 are more flattened and that the branches of the saddles in the suture 

 are more delicate than in P. vidriensis. It should be noticed that the 

 third auxiliary saddle in our species is on the umbilical seam, while in 

 P. vidriensis it is on the umbilical wall. 



P. HUH is easily distinguished by its manner of involution, its gen- 

 erally greater width and its much smaller umbilicus; also the saddles 

 on its suture are much stouter than in our species. 



P. Cumminsi is entirely different with respect to the ratio of dimen- 

 sions, and the umbilicus seems to be still wider than in our species ; the 

 suture is very different. 



Age: 



Lower part of Leonard formation, Permo-Carboniferous.^ 



^Through an error Udden (Univ. Texas Bull. 1753, p. 46) has cited the rest of the 

 fauna occurring together with P. compressus as belonging to the Hess formation. 



