Permo-Carboniferous Ammonoids of the Glass Mountains 



III 



the surface, broad, beginning at the umbilical seam where they are 

 narrow and rounded, widening and flattening on the flank and disap- 

 pearing when they reach the venter. They are practically straight but 

 lean forward from the umbilicus on. On the next smaller whorl the 

 ribs are similar to those on the largest whorl, with the single exception 

 that they lean a little less forward and that they are still more promi- 

 nent. On the whorl which follows the second one, the ribs look nearly 

 like broad, elongated, radial tubercles. Interstices with a rounded bot- 

 tom, and about as wide as the ribs, separate these from each other. 

 The venter is smooth. The suture is unknown. 



Dimensions: 



Diameter : about 21.0 mm (1) 



Width 4.0 0.19 



Height of the last whorl 6.2 0.30 



Diameter of umbilicus, about 9.0 0.43 



Relation to other species: 



Our specimen has a great general resemblance to the inner whorls 

 of P. elegans Girty, although it does not seem to have any sigmoidal 

 ribs. The cross-section is certainly different from that of the Guada- 

 lupian form, which is rather more parabolical than elliptical, thus 

 causing a pretty steep umbilical wall at least in the largest wall, while 

 in our specimen the umbilical wall is not steep at all. The ventral 

 portion of P. elegans is much more broadly rounded than in our species. 



Girty compares his species with P. Hoeferi and P. Halli but it seems 

 to resemble still more P. plicatus Gemm.^ although in this latter species 

 the ribs are still wider apart. That Gemmellaro's specimen does not 

 show the finer ribbing on the outer whorl does not prove that it does 

 not exist in the largest whorl, because the figured specimen is very 

 small and certainly does not represent more than inner whorls. Its 

 cross-section is similar to that of the Guadalupian form and quite dif- 

 ferent from that of our outer whorl, although a little more like that 

 of our next smaller whorl. The number of ribs in the Sicilian species 

 is probably equal to that of our species, but smaller than that of P. 

 elegans when counted on the whorls corresponding in size. 



Our species is certainly different from P. elegans as well as from 

 P. plicatus but belongs to the same group. 



'Gemmellaro, Calc. c. Fusulina, app. p. 21, pi. D, fig. 22, 23. 



