Permo-Carboniferous Ammonoids of the Glass Mountains 187 



developed from our form, because in general form the lateral and 

 auxiliary lobes and saddles are quite similar, and it may be easily 

 thought that in the younger form the external saddle simply was a 

 little more highly developed. Very characteristic in both species is 

 the great difference in length between the first and second auxiliary 

 lobes. We shall see later on that there exists a still younger form 

 which may have developed- from M. Copei. No other species in 

 Texas or elsewhere shows any marked relationship with our species. 



Perrinites n. sp. 



Shell moderately involute, flattened ,on the flanks and strong'ly 

 rounded on the venter. Cross-section of the whorl elliptical, much 

 broader than high. The greatest width is a little above the umbilical 

 border in medium-sized specimens, but in very young ones and in the 

 completely mature forms the greatest width is at the umbilical border. 

 Older specimens appear to have had a much higher whorl than very 

 young ones. Flanks flattened on the third nearest the umbilical bor- 

 der, while in the upper two-thirds they are strongly convex and pass 

 in a continuous curve into the rounded venter. Umbilicus moderately 

 narrow and very deep, the umbilical border moderately sharp, slightly 

 rounded; no real edge exists. Umbilical wall very steep and rather 

 broad, nearly vertical. 



The casts are smooth, the shell shows an ornamentation by extraor- 

 dinarily numerous broad, flat, fine, transversal ribs, which on the flank 

 are slightly curved backwards and which on the venter form a dis- 

 tinct curve backward, so that their fore side appears slightly concave. 

 The transversal ribs or lines are separated from each other by very 

 fine, deep, extrem|ely narrow depressions. This ornamentation is ap- 

 parently less delicate than the similar one seen in the other species so 

 far described. 



The septa stand very near each other, the saddles of the older suture 

 touching the sides of the lobes of the next younger line. The suture 

 is relatively quite complicate; between the sipho and the umbilical 

 border it follows in general a straight line. The suture which shall be 

 described here belongs to a mature specimen (height of the whorl 

 about 25 mm. ) and is the first complete one between the sipho and the 

 umbilical seam that has been described sj far. It is not essentially 



