A New Ammonite Fauna of the Lower Turanian of Mexico 229 



INOCERAMUS Sowerby 



INOCERAMUS LABIATUS Schloth-aim 



PI. 20, fig. 5 



1813: Oxtracites labiatus Schlotheim in Leonhard's min. Taschenb. VII p. 93, fide 



Geinitz. 



1875: Inoceramus labiatus Geinitz, Elbthalgebirge II, p. 46, pi. 12 cum syn. 

 1893: Inoceramus labiatus Stanton, Colorado Form., p. 77, pi. 10, fig. 4; pi. 14, fig. 2 



cum syn. 

 1903: Inoceramus labiatus Petrascheck, Inoc. a. Kr. Bohmens, p. 156. 



In the upper horizon of the Salmurian of Cerro del Macho, Dr. Haar- 

 mann found four Inoceramus of which at least three are typical Inoceramus 

 labiatus Schlotheim. They are relatively small individuals but are en- 

 tirely identical with those from Parras, Mexico, and different European 

 localities. I have discussed this species extensively in Boletin 30 of the 

 Institute Geologico de Mexico; a detailed description of the specimens 

 found on Cerro del Macho does not seem to be necessary. 



The occurrence of this species at our locality is of some importance 

 because the determination of the age of the Mexican Turonian beds up 

 to the present is entirely founded on bivalves, especially Inoceramus, and 

 this class of fossils is always stratigraphically of less value than the 

 cephalopods. My former determinations are now confirmed by the. oc- 

 currence of Inoceramus labiatus together with typical ammonites of the 

 lower Turonian. 



Up to the present, Inoceramus labiatus has not yet been found in the 

 lower beds of our Salmurian ; it only occurs in the upper one, and even 

 there it is not very frequent. Of course we can not yet draw any con- 

 clusions from this distribution. The stratigraphical conditions of the 

 region of Mohovano should first be studied with care, larger collections 

 from the lower horizons should be made, so as to show if Inoceramus 

 labiatus really does not appear in those beds ; and finally the relation be- 

 tween the cephalopod beds and the shales with Inoceramus of other re- 

 gions of northern Mexico should be ascertained. 



Number of specimens: 3 (4?). 



Age: Lower Turonian (Salmurian), upper horizon. 



