A New Ammonite Fauna of the Lower Turanian of Mexico 207 



nodules near and on the ventral part. These nodules form two rows, each 

 of which is composed of 16 to 17 nodules on the last whorl ; those of the row 

 on the ventral portion are a little elongated longitudinally. Thus we find 

 on each side of the shell three rows of nodules : the umbilical, the interme- 

 diate and the ventral row. It seems that the nodules of the intermediate 

 row increase in thickness in the front part of the whorl, while those of the 

 ventral row decrease a little and extend themselves more longitudinally, 

 but none of the specimens is large enough to show the development of the 

 nodules in an advanced age. Between the two ventral rows we observe a 

 narrow concave zone in the inner whorl and a nearly flat one on the exter- 

 nal whorl. 



The suture is very much destroyed but its main features can still be 

 recognized. The external lobe is rather deep and narrow, ending in two 

 branches ; the external saddle is broad and high, divided into two branches 

 by an adventive lobe of relatively great depth ; the first lateral lobe is deep 

 and ends in two points ; the first lateral saddle is apparently broad but its 

 exact form can not be recognized because the shell is much destroyed in 

 this part. 



Dimensions: 



Diameter 87.0 mm. (1) 



Height of the last whorl 33.0 mm. 0.38 



Width of the last whorl 42.0 mm. 0.48 



Diameter of the umbilicus 23.0 mm. 0.26 



Height of the last whorl in the same diameter but half a whorl 



backwards 30.5 mm. 0.35 



Width of the last whorl in the same diameter and half a whorl back- 

 wards 39.0 mm. 0.46 



Our species certainly belongs to the group of Mammites nodosoides 

 Schlotheim. Its suture coincides in general fairly well with the one figured 

 by Laube and Bruder 1 , but its form and ornamentation resemble more that 

 of Mammites conciliatus Stoliczka, 2 which differs from the type of the group 

 especially by the greater thickness of the whorl and the more numerous 

 nodules on the ventral portion. 



Our species differs from Mammites conciliates by its more involute 

 form, the external whorl covering nearly two-thirds of the preceding one. 

 barely leaving uncovered the row of umbilical tubercles. We find another 

 difference in the number of intermediate and ventral nodules, which is 

 much less in our specimen than in the species of Stoliczka. In this direc- 

 tion our individuals resemble more the type of Mammites nodosoides, but 



'Laube und Bruder. Amm. d. bohm. Kreide, p. 230. 



2 Stoliczka, Ceph. Cret. Rocks India, p. 99. pi. 50, fig. 4; pi. 51, fig. 1. 



