372 The American Geologist. December, 1902. 
usual order. The entire shell must have been about 125 mm. 
in diameter. 
In none of the specimens are the sutvu^es shown. 
The above named fossils are referred to the Upper Jnr- 
assic by Castillo and Aguilera. This points to the presence 
of Upper Jurassics limestones and bituminous and limy shales 
near San Pedro del Gallo, state of Durango, Mexico. In the 
Bosquejo Geologico de Mexico* it is stated that the Upper 
Jurassic and Cretaceous series occurs in the north-central part 
of the state of Durango, being fossiliferous in the vicinity of 
the town of Gallo. but that lack of data would not permit the 
classification (separation) of this formation. It is believed 
that the town of Gallo here referred to, and shown on the map 
about fifty miles slightly southwest of Mapimi, is the same 
as the San Pedro del Gallo from which our fossils come. 
The abbreviation of such names is usual, and Mr. Tuttle 
himself speaks of the town simply as Gallo in one place in his 
letter. 
On the geological map of Mexico published in i88g under 
the direction of professor Castillo, a small portion of the map 
in the vicinity of Gallo is colored blue, indicating Jurassic at 
this point. In the revised edition of this map, however, "re- 
formada con nuevos datos en 1891, 1892 y 1893," no Juras- 
sic is shown at this point at all. Cretaceous alone being repre- 
sented. It would appear that the "new data" led to the rejec- 
tion of the idea of the Jurassic's occurring in this locality. If 
such is the case, the present note may serve tO' confirm th.e 
correctness of the older map in this regard. 
Palaeontological Laboratory, 
Columbia University, 
November 18, ipo2. 
* Bol. Inst. Geol. Mex., Nos. 4, 5 y 6, p. 20.) 
