A New Ammonite fauna of the Lower Turanian of Mexico 185 



Horizon I. 



Upper 



Cenomanian Turonian 



Species from Cerro del Macho Related species 



Metoecoceras aff. Whitei Hyatt M. Whitei Hyatt ? T 



Metoecoceras n. sp. M. Geslianum Petrascheck + 



Exogyra Haarmanni n. sp. 



Exogyra cfr. olisiponensis Sharps Ex. olisiponensis Sharpe + + 



Hemiaster sp. 



The age of this horizon cannot be determined quite exactly. The fossils 

 are few, the cephalopods among them indicate only that the horizon belongs 

 either to the lower Turonian or the upper Cenomanian. Metoecoceras aff. 

 Whitei is similar to forms found in the Colorado Formation of the United 

 States, a division which up to now has not been subdivided stratigraphic- 

 ally with the necessary exactness ; it probably represents in its larger part 

 the Turonian, but may possibly contain some upper Cenomanian and a por- 

 tion of Emscherian. The portion in which M. Whitei has been found be- 

 longs to the lower part of the formation, which is either the lower Turonian 

 or the upper Cenomanian. Our Metoecoceras n. sp. is very similar to M. 

 Geslianum Petrascheck, 1 which occurs in the upper Cenomanian of Saxony, 

 but we do not know exactly if our specimen has been found in this lowest 

 horizon or in one a little higher. 



Interesting is the occurrence of an Exogyra certainly belonging to the 

 group of Exogyra olisiponensis Sharpe. This species is found on the bor- 

 der of the Mediterranean in the Cenomanian as well as in the Turonian, 

 although the variety which is most similar to our specimen seems to be 

 limited principally to the Cenomanian. Our Exogyra Haarmanni n. sp. is 

 a new species and not very characteristic, therefore without any strati- 

 graphic value. The Hemiaster found in the same bed can not be used for 

 the determination of the age as it does not appear to be identical with any 

 described species nor to be closely related to any known species which 

 might indicate the age of these beds. 



The small number of fossils of this horizon does not allow an exact de- 

 termination of its age. Taking into consideration the radical difference be- 

 tween the character of this fauna and that of Horizon II, and the presence 

 of a form of Metoecoceras very similar to the one of the upper Cenomanian 

 of Saxony, I feel inclined to consider this horizon provisionally as upper 

 Cenomanian until other and more characteristic fossils allow a more exact 

 determination of the age. 



Much more numerous is the fauna of Cephalopods in Horizon II and 



iPetrascheck. Amm. d. sachs. Kreideform., 1.140 (10) pi. 7 (1) ; figs. 3-5. 



