A New Ammonite Fauna of the Lower Turanian of Mexico 225 



may have been changed and that the fossils frequently have not been col- 

 lected with the necessary exactness. 



Number of specimens : 1. 



Age: Lower Turonian (Salmurian), lower horizon. 



HOPLITOIDES V. Koenen Emend. Solger et Pervinquiere 



The genus Hoplitoides has been established by von Koenen 1 for certain 

 ammonites from the limestones of the Mungo in Kamerun; later Solger 2 

 studied the same fauna and made the definition of the genus more precise. 

 Then Pervinquiere 1 amplified this definition still more and distinguished 

 two groups within the genus Hoplitoides: the bicarinate and the monocar- 

 inate forms. The first group seems to be limited to the Turonian, the sec- 

 ond one to the Emscherian. 



Among our material we find a few ammonites which very probably be- 

 long to the first group, the bicarinate Hoplitoides. The specimens are not 

 very well preserved and the generic determination is not entirely certain. 

 The external form corresponds completely with that of the Hoplitoides, 

 but the suture is much destroyed and scarcely permits recognition of the 

 general character of the line; this, however, coincides entirely with the 

 suture of the bicarinate Hoplitoides. The character of the suture on the 

 other hand shows that the specimens do not belong to Placenticeras, a 

 genus which externally is quite similar to Hoplitoides. 



HOPLITOIDES aff. MIRABILIS Pervinquiere 



PI. 19, figs. 1-3 

 1907 : Hoplitoides mirabilis Pervinquiere, Paleontologie Tunisienne, p. 218, pi. 10, fig. 3 



Among the material placed at my disposition I found two relatively 

 complete specimens and four fragments which, according to their suture 

 and external form, belong to the so-called Pseudoceratites of the Creta- 

 ceous. The best preserved specimen shows the following features : 



Shell discoidal, entirely evolute, with whorls of lanceolate cross section 

 truncated at the point, much higher than broad. The umbilicus is very 

 narrow, the umbilical wall is vertical and the umbilical border rounded. 

 The flanks are smooth, very little convex, nearly flat. The venter is flat 

 with a sharp shoulder on each side; on the internal whorl we observe on 

 both shoulders of the venter a sharp keel and the zone there is concave. 



J v. Koenen, Nachtr. Foss. Mungo i. Kamerun, p. 53. 

 2 Solger, Mungokreide, p. 127. 



