Permo -Carboniferous Ammonoids of the Glass Mountains 89 



bilical shoulder ; whorl not much broader than high. Umbilicus mod- 

 erately, wide and shallow, umbilical wall not very steep, umbilical 

 shoulder not very sharp but rather rounded. No constrictions visible 

 on the shell (cast unknown). 



The ornamentation of this species (pi. Ill, fig. i, 3) is very charac- 

 teristic. There are about twenty-five transversal ribs which begin, 

 at the upper end of the umbilical wall, cross the umbihcal shoulder and 

 disappear rather suddenly a little below the middle of the flank. These 

 ribs are all slightly inclined forward, and are crossed by some spiral 

 ribs which cause about three tubercles on each of them. The trans- 

 versal ribs are comparatively high and sharp but not very broad ; they 

 are separated from each other by wide and deep furrows with round 

 bottom. The spiral ribs mentioned appear not only on the trans- 

 versal rib but on the whole flank and the ventral region. There are 

 seven ribs on each flank; they are relatively thin and high, sharp, 

 and separated from each other by wide and round furrows. On the 

 ventral part there are about six ribs (three on each side of the 

 sipho) which stand m'uch nearer together than those on the flanks. 

 Near the last part of the whorl a new rib begins between the fifth and 

 sixth rib on the flank (counted from. the umbilicus), which indicates 

 that larger specimens would show a larger number of spiral ribs. 



The septa of this species are unknown. 



Dimensions : ^ 



Diameter 25.7 mm (1) 



Width 10.0 0.39 



Height of last whorl 9.5 0.37 



Diameter of umbilicus : 



From seam to seam 8.5 0.33 



From shoulder to shoulder 11.8 0.46 



Relation to other species : 



Although it was not possible to find the suture of this species there 

 does not remain any doubt about its belonging to Gastrioceras and es- 

 pecially to the group of G. Zitteli Gemm. None of the species so far 

 described is very similar to ours, the nearest being perhaps Gastrio- 



^The dimensions were not measured at the place of the largest diameter, because 

 the specimen! is somewhat crushed there. 



