164 University of Texas Bulletin' 



saddles is unknown. This internal suture is taken from a fairly 

 mature specimen. 



Dinietisions:^ 



I II in 



Diameter 125.7 mm (1) 102.6 mm (1) 63.4 mm (1) 



Width 58.1mm 0.46 49.5 mm 0.48 3b. 4 mm 0.53 



Height of last whorl 67.5 mm 0.54 54.1 mm 0.53 33.5 mm 0.53 



Diameter of umbilicus ... . 15.0 mm 0.12 13.0 mm 0.13 6.7 mm 0.11 



IV V VI 



Diameter 56.6 mm (1) 44.8 mm (1) 43.1mm (1) 



Width 30.7 mm 0.54 25.0 mm 0.55 24.1 mm 0.56 



Height of last whorl 30.0 mm 0.53 23.6 mm 0.53 23.5 mm 0.54 



Diameter of umbilicus.... 6.2 mm 0.11 5.0 mm 0.11 4.1 mm 0.10 



VII2 VIII IX 



Diameter 36.1 mm (1) 29.0 mm (1) 16.5 mm (1) 



Width 20.7 mm 0.57 16.5 mm 0,57 10.2 mm 0.62 



Height of last whorl 18.7 mm 0.52 15.0 mm 0.52 8.0 mm 0.48 



Diameter of umbilicus... 4.1 mm 0.11 ?4.0 mm 0.14 ?3.0 mm 0.18 



X XI XII 



Diameter 13.0 mm (1) 7.6 mm (1) 4.4 mm (1) 



Width 8.0 mm 0.62 5.7 mm 0.75 2.9 mm 0.66 



Height of last whorl 5.3 mm 0.41 3.4 mm 0.45 1.8 mm 0.41 



Diameter of umbilicus... 1.1 mm 0.085 0.6 mm 0.08 0.4 mm 0.09 



Relation to other species: 



A^ery nearly related to our species is P. HUH Smith. ^ It is a little 

 more involute, its cross section is less elliptical than that of our speci- 

 mens of the same size; the saddles of the suture are a little stouter, 

 and the lobe narrower than in our species; the points in which the 

 lobes end are somewhat shorter in P. Hilli than in P. vidriensis. 

 These dififerences are relatively small, but one cannot expect great 

 variety in such a simply built genus as the present one. 



Less similar yet is P. Cumminsi White,* the whorls of which are less 

 high, while the ufnbilicus is much larger than our species. 



^In the very small specimens the measurements, especially those of the umbilicus, 

 are not entirely exact, on account of the relative coarseness of my instrument. 



"While all the rest of the measured specimens come from a point about two miles 

 west-northwest of Iron Mountain, this one comes from a point three miles north at 

 the old- oil derrick on Wedin's Ranch on the north side of "Round Point ridge," 

 Glass Mountains. 



•J. P. Smith, Carb. Amm. of N. America, p. 140, pi. 27. 



*Ch. A. White, The Texan Permian, p. 20, pi. 1, fig. 4-8. 



