370 The American Geologist. December, 1902. 
ON SOME JURASSIC FOSSILS FROM DURANGO, 
MEXICO. 
By Douglas Wilson Johnson, New York. 
While making an examination for coal in certain form- 
ations \\;est of Mapimi, state of Durango, Mexico, Edgar F. 
Tuttle, E. ^I., secured a few fragments of ammonoids which 
were sent to the Geological Department of the Columbia l"ni- 
versity. These fossils were given to the writer for identifi- 
cation, and the following notes are offered regarding their 
occurrence and age. 
Quoting from Mr. Tuttle's letter, the fossils were found 
at San Pedro del Gallo, a town about fifty miles west of 
Mapimi, occurring in limestone near an underlying bed of 
bituminous and calcareous shale. This shale is exposed over 
a considerable area, and consists of alternate thin layers of 
the bituminous and lini}' material, the former fometimes be- 
coming tjuite thick, and where exposed by shallow wells, 
smelling perceptibly of the bituminous matter. The town of 
Gallo is situated at the western border of the area over which 
the shales are exposed, (the area being some four thousand 
feet across the strike), near the contact with the limestone 
band in which the fossils occur. The whole formation has a 
westerly dip. The fossils are few and fragmentary. 
Of the four ammonoids sent by 3ilr. Tuttle one fragment 
is too poorly preserved to admit of identification. The costae 
are simple, broad and rounded, and show uncertain evidence 
of terminating in nodes along the ventro-lateral angle, while 
even more uncertain is the possible occurrence of nodes mid- 
way between this and the umbilical angle. The w'riter can 
find no type to which the af^parent features of this fragment 
correspond, and is inclined to regard it as a new species, al- 
tho it is too badly worn and broken to be determined with 
certainty. 
Another fragment, well preserved as to detailed features, 
but too small to show distinctive characters, is evidently one 
of the Perisphinctidae, possibly Perisphinctes potosinus Cas- 
tillo and Aguilera, described from Rancho Alamitos, Sierra de 
Catorce, San Louis Potosi.* The costae are compressed and 
* "Fauna Fossil de la Sierra de Catorce. San Louis Potosi," por Antonio 
del Castillo y Jose G. Aguilera. Boletin del Instituto Geologtco de Mexico, 
Num. 1, p. 31, lam. xvii, fig. 1; lam. xxiv, fig. 2. 
