A New Ammonite Fauna of the Lower Turanian of Mexico 209 



abrupt. The ornamentation consists in widely separated, low, rounded, 

 nearly straight ribs which begin in a nodule at the umbilical border and 

 which end in another very high and pointed nodule at the ventral shoulder. 

 Between the two rows of nodules on the ventral part we observe a broad, 

 slightly convex and smooth zone. In the last half whorl we count five ribs. 

 The suture is not visible. 



Dimensions: 



Diameter 280mm. (1) 



Height of the last whorl 117 mm. 0.42 



Width of the last whorl 94 mm. 0.34 



Diameter of the umbilicus 104 mm. 0.37 



Our specimen certainly belongs to the group of Pseudaspidoceras Foot- 

 eanum Stoliczka, 2 but differs from it by its cross-section which is much 

 higher than wide. This is not an absolutely distinctive character because 

 we should take into consideration the large size of our specimen and we 

 do not know the latest development of the species of Stoliczka. Our speci- 

 men resembles Pseudaspidoceras Footeanum Petrascheck more than it 

 does the type. The cross-section of the species of Petrascheck is more 

 similar to ours and also has widely separated ribs. 



The group of Pseudaspidoceras Footeanum Stoliczka has a very wide 

 distribution; it is represented in all the northern part of Africa (we in- 

 clude in this group Ps. salmuriense) , in Nigeria, in Portugal, in Saxony, 

 and in India. 



Number of specimens : 1. 



Age: Lower Turonian (Salmurian), lower horizon. 



PSEUDASPIDOCERAS aff. PEDROANUM Whit^ 

 PL 13, fig. 1; PL 15, fig. 1 



1887: Ammonites Pedroanus White, Brazil, p. 212, pi. 22, figs. 1, 2 (not pi. 20, fig. 3). 



In the lower horizon of the Turonian of Cerro del Macho we find a large 

 and relatively well preserved specimen which belongs to the group of 

 Pseudaspidoceras Footeanum Stoliczka. Its features are: 



Shell large with whorls of a subquadranglar cross-section, nearly as 

 high as wide. The flanks are flattened, the ventral portion is nearly flat. 

 The umbilicus is relatively wide and deep, the umbilical wall is vertical 

 but without a sharp umbilical shoulder. The external whorl covers only 

 the ventral portion of the preceding one and leaves the nodules of the ven- 

 tral shoulder free. The ornamentation consists of extremely low and 



2 Stoliczka, Ceph. Cret. Rocks India, p. 101, pi. 52, figs. 1, 2. 



