Permo-C arboniferous Ammonoids of the Glass Mountains 91 



The ornamentation of this species is extremely characteristic; it 

 consists of a great number of transversal ribs on the flank. These 

 begin at the umbilical seam, and are slightly bent forward. They are 

 straight on the, lower two-thirds of the flank and then curve strongly 

 forward and end at the ventral shoulder. These ribs are high and 

 sharp, steeper on the back side than on the fore side. On the ventral 

 region we observe six spiral ribs, three on each side separated by a 

 somewhat broader furrow along the sipho. Another very faint rib 

 shows where the transversal ribs end. The spiral ribs are low and 

 ronnded, separated by relatively narrow furrows. 



A remnant of the suture line is visible on one flank and as far as it 

 goes, corresponds to that of Gastrioceras. 



Dimensions: 



Diamelter 33.6 mm (1) 



Width 10.3 0.31 



Height of last whorl 9.0 0.27 



Diameter of umbilicus between the seams . . . 17.7 0.53 



Relation to other species : 



There does not remain much doubt that the present species belongs 

 to Gastrioceras although the suture line is very imperfectly known ; es- 

 pecially the form of the siphonal lobe could not be observed. 



Among the Russian and Sicilian' species there is none which could 

 be confounded with our form. It may perhaps be related to Gastrio- 

 ceras Waageni Gemm.^, but the transversal ribs are not by far as high 

 in that species as in ours, and the spiral ribs are not limited to the ven- 

 tral portion but cross over the transversal ribs as in our G. altudense. 



There is only one species very similar to ours and that is Gastrio- 

 ceras sp., described by Girty^ from the Delaware Mountain formation. 

 This species shows the transversal ribs passing over a great part of 

 the flanks, while spiral ribs cover the ventral portion. Girty's species 

 is much less evolute than ours and the number of transversal ribs 

 is much smaller so that there is no doubt about their being specifically 

 different. 



Our species is certainly a new one and possibly even the representa- 

 tive of a new group, as the relationship to that of G. Zitteli is not a 



'Gemmellaro, Calc. c. Fusulina, App., p. 25, pi. D, fig. 24-26. 

 'Girty, Guadalupian fauna, p. 500, pi. 29, fig. 22. 



