A New Ammonite Fauna of the Lower Turanian of Mexico 191 



with the cephalopod beds described here ; neither have those beds with Ino- 

 ceramus labiatus been found in immediate contact with fossiliferous beds 

 of the Emscherian. Only in one place, Opal, Zacatecas, I have found beds 

 with Inoceramus labiatus (rare) and /. hercymicus (very frequent) in 

 contact with sandstones containing an Inoceramus nearly related to Inoce- 

 ramus cycloides, but the cross section of this locality is too incomplete and 

 the fauna too poor for a decision of this rather important problem. 



The locality of Cerro del Macho is stratigraphically important in so far 

 as it gives us some data for the limitation of the upper Cenomanian and 

 the lower Turonian. In a former work we have been able to subdivide the 

 Cenomanian of Cerro de Muleros near Ciudad Juarez, but we have not been 

 able to find fossils in the sandstones between the beds with Inoceramus 

 labiatus and the marls with Hemiaster'Calvini; thus it was impossible to 

 decide if those sandstones belonged to the Cenomanian or the Turonian. 

 In the present case we have very fossiliferous beds very near the limit be- 

 tween the Cenomanian and the Turonian. The fossils of the Cenomanian 

 are very different from those found up to the present in Cenomanian rocks 

 of Mexico. Of especial importance is the occurrence of Metoecoceras. 

 The Turonian ammonite fauna is also entirely new for Mexico, the few 

 ammonites so far found in the beds with Inoceramus labiatus belonging to 

 entirely different groups. 



Haarmann has distinguished two horizons, II and III, but these do not 

 appear to be more than local subdivisions notwithstanding the circum- 

 stance that the fauna of the two beds seem to be rather different. We must 

 not give too much importance to this circumstance, as the collections so far 

 made are still rather small and the aspect of the fauna may change alto- 

 gether with larger collections made. As far as we can see, the lower bed 

 contains principally cephalopods while in the upper one bivalves and gas- 

 tropods predominate. 



With respect to the conditions of life in this locality we may say with 

 some certainty that at the end of the CeYiomanian in the Cerro del Macho 

 region as well as in others of northern Mexico, especially in the State of 

 Chihuahua, there existed a littoral facies or at least a very shallow sea; 

 this is indicated by the great quantity of Ostreidae which nearly form beds 

 or which have been carried away from neighboring beds. At the begin- 

 ning of the Turonian age the sea seems to have deepened a little, the pre- 

 dominance of the ammonites and the absence of littoral bivalves indicating 

 a less shallow sea. It is probable that during the time of the deposition of 

 the upper part of the Salmurian the sea again became a little shallower; 

 this is indicated by the predominance of Lamellibranchia and Gastropoda 

 with thick shells, but the facies is not quite as much a littoral one as in 



