Per mo -Carboniferous Ammonoids 'of the Glass Mountains 141 



Age: 



Wolfcamp division, lowest Permo-Carboniferous. 



Number of specimens examined: 



One. The only one which has been found so far. 



Locality: 



Immediately northwest of Wolf Camp, Glass Mountains. 



Marathonites vidriensis nov. sp. 

 PI. VII, Fig. 5-32 



Shell small, of discoidal but rather globose involute form, with 

 somewhat flattened flanks which curve into the not very convex ven- 

 tral portion; the cross-section is more rounded trapezoidal than semi- 

 lunar. The greatest width lies a little above the umbilical border. The 

 spire is formed by numerous and very slowly growing whorls about 

 twice as broad as high. The flank curves slightly down to the border 

 of the umbilicus, from there the shell bends sharply into the nearly 

 vertical umbilical wall, which is relatively broad. The umbilicus is 

 moderately narrow and very deep. All the whorls show deep trans- 

 versal constrictions on the cast, about four in number on each of 

 them. These constrictions are nearly straight on the inner whorls and 

 only bend very slightly backward on the larger ones; on one of the 

 specimgns the shell is preserved. There the constrictions show also 

 on the outer surface, but are accompanied by slight varices on their 

 forward border. 



The shell shows an ornamentation composed of very thin elevated 

 transversal striae separated from each other by rather broad flat in- 

 terstices which taper toward the umbilicus and become very narrow 

 there. The same ornamentation shows also on the interior surface 

 of one of the whorls. 



The sutural Hne (pi. VII, fig. 8, 15, IQ, 26, 30) is nearly straight, 

 and only bent a little backward near the siphonal region on the ventral 

 side, and much so in the antisiphonal portion of the internal side. The 

 septa are moderately near together, without touching each other. All 

 the saddles are entire, very high, slender, rounded at the top and 

 slightly constricted near their bas^. The lobes are generally broader 



