Permo-Carboniferous Ammonoids of the Glass Mountains t6i 



Perrinites vidriensis nov. sp. 

 PI. VIII, Fig. i-io; PI. IX, Fig. i-io; PI. X, Fig. 1-21 



Shell discoidal, involute, with compressed flanks and rounded ven- 

 ter ; greatest width at the umbilical shoulder in smaller specimens, and 

 a little above in the larger individuals. Whorls not very deeply em- 

 bracing, the involution being in the smaller whorls a little more than 

 one-third of the height, and in the largest ones a little less than one- 

 half of the height of a whorl. The cross-section is parabolical to 

 elliptical, the height being greater than the width. There are four 

 to six constrictions on the whorl, straight to slightly sinuous on the 

 flank and strongly curving on the venter, with the convexity toward 

 the back. The constrictions are deep on the cast, while on the shell 

 they are noticeable by a thickening of the lines of growth on both sides 

 of it ; almost no depression is visible on the shell. The ornamentation 

 consists of Very fine lines of growth entirely parallel to the constric- 

 tions. The umbilicus is narrow, and the umbilical shoulder is com- 

 paratively sharp in the younger whorls, while in the older ones it be- 

 comes considerably rounded. The umbilical wall is steep and broad, 

 although not perpendicular. The body chamber is unknown; even 

 specimens with a diameter of 125 mm. do not show its beginning. 



The septa are very near and often even almost touch each other in 

 certain parts. The suture (pi. VIII, fig. 4, 7; pi. IX, fig. 10; pi. X, 

 fig. 19) follows a straight line between the sipho and umbilicus. The 

 siphonal lobe is divided in two branches by a high median saddle. 

 Each of the branches ends in a long and sharp point. It tapers from 

 the upper part toward the bottom. The first lateral lobe is scarcely 

 deeper than the branches of the siphonal lobe ; it is generally somewhat 

 broader and more symmetrical and a little more scalloped. The second 

 lateral lobe is similar to the first, but also deep and wide. The three 

 auxiliary lobes are similar to the lateral ones, but decrease gradually 

 in depth and width, as all the lobes do from the first lateral to the 

 umbilicus. The third auxiliary lobe is on tlie umbilical shoulder. 



The median saddle of the siphonal lobe is very high, broader at 

 the base than at the top, where it is notched by an indentation. . In a 

 mature specimen (130 mm.) it has three secondary lobes on each side 

 and several rudimentary ones; in those somewhat smaller (65 mm.) 

 it shows only the three secondary lobes and in smaller whorls it loses 



