A New Ammonite Fauna of the Lower Turanian of Mexico 223 



specimen is not possible on account of its small size ; we can only say that 

 it is a Neoptychites similar to Neoptychites cephalotits but probably a dif- 

 ferent species. 



Neoptychites cephalotus occurs in the lower Turonian of Tunis, Altrerla 

 and France. Grossouvre proposes to unite it with Neoptychites Telinga. 

 Stoliczka and Pervinquiere accepts this opinion. There is no doubt that 

 the adult individuals of the two species resemble each other very much, 

 although the suture seems to be somewhat different and a little more rami- 

 fied in N. cephalotus; but this last character is not decisive as long as we 

 know only the suture of a very large specimen of N. Telinga.. A definite 

 result can only be reached through the study of the development of N. Te- 

 linga or at least of that of small specimens. 



Number of specimens : 1. 



Age: Lower Turonian (Salmurian), upper horizon. 



NEOPTYCHITES aflf. XETRIFORMIS Pervinquiere 

 PL 18, figs. 9, 11 



1907: Neoptychite xetriformis Pervinquiere, Paleontologie Tunisienne, p. 398, pi. 27, 

 figs. 5-7. 



Among the material collected by Dr. Angermann is a very typical Neop- 

 tychites. The specimen is sufficiently well preserved for a generic deter- 

 mination. Its features are : 



Shell discoidal, very involute, with whorls of nearly sagittiform cross 

 section, much higher than broad. The greatest width is near the umbilical 

 border. The flanks are quite flattened and very little convex, and the ven- 

 ter is rounded. The umbilicus is extremely narrow and deep ; the umbil- 

 ical wall is vertical ; apparently a slight thickening exists on the umbilical 

 border, at least in the last part of the external whorl. On the flanks we 

 observe radial, broad, low, and rounded ribs which are strongest in the 

 region near the venter and which decrease in strength toward the umbilical 

 as well as toward the ventral region ; they disappear near the umbilicus. 

 On the venter the ribs are very low and scarcely discernible ; near the ven- 

 tral portion, they bend forward. The number of ribs could not be counted 

 because part of the surface is corroded. 



The suture is not very well preserved but the main features can be rec- 

 ognized. The external lobe is relatively wide and shallow, ending in two 

 short branches; the external saddle is not very high nor very broad but 

 little ramified. The first lateral lobe is wide and ends in two points ; it also 

 has a branch on each side, and is deeper than the external lobe. The first 



