Pernio-Carboniferons Ammonoids of the Glass Mountains 77 



All of our specimens are casts and not a trace of sculpture is 

 visible. There were certainly no tubercles on the keels, or ribs on 

 the flanks, even of the inner whorls. 



There exists a certain difference in the form of the largest and the 

 smallest specimens. While the flanks of the large whorls are evenly 

 convex, those of the small ones (20 mm. diameter) are almost per- 

 fectly flat on the four-fifths of the flank nearest to the umbilicus and 

 they then bend rather suddenly over toward the siphonal region, as 

 is shown in our cross section on pi. I, fig. 48. 



The septa are not very near together but the lobes almost touch 

 the saddles of the next smaller septum. The suture follows a sig- 

 moidal line. The mature suture (compare text fig. 2 and pi. II, fig. 2) 

 consists of a very great number of lobes and saddles. The siphonal 

 lobe, S, is very deep, with parallel sides, and extremely narrow. It 

 occupies about the width of the median groove on the venter and ends 

 in two points. The two lateral lobes, Li and L^, are divided in two 

 branches by a high secondary saddle; the first lobe is asymmetrical, the 

 branch on the umbilical side being longer than that on the other one, 

 and straight ; while the branch on the siphonal side is curved with the 

 convexity toward the venter. The second lateral lobe is almost sym- 

 metrical. There are ten auxiliary lobes, the first one of which (ai) is 

 at least as deep as the second lateral lobe and entirely similar in shape. 

 The first six auxiliary lobes, ai-ae, resemble in general shape the sec- 

 ond lateral lobe, although they decrease rapidly in depth and the divid- 

 ing secondary saddle becomes quickly lower and broader; in the 

 seventh and eighth, and even in the ninth, the division in two branches 

 is at least still indicated, while the tenth lobe shows a rounded bottom. 



The external saddle, Es, is divided in two parts, Esi and Es2, by 

 the adventive lobe, A. The branch Esi is very asymmetrical and 

 strongly scalloped by nine rudimentary adventive lobes ; those on the 

 umbilical side are much deeper than those on the siphonal side. All 

 the rudimentary lobes form a right angle with the direction of Esi, 

 with the exception of «9, which is in an oblique position. As I have 

 already said, in the description of M. Whitneyi, I would prefer to 

 consider this lobe, "9, as a part of A than as an independent rudimen- 

 tary adventive lobe. The umbilical branch, Es2, of the external saddle 

 is nearly parallel to Esi. Its form is slightly trilobate like the lateral 



