PUBLICATIONS. 859 
characteristic forms that are common in the more accessible localities. 
The introductory pages are devoted to a brief review of previous 
Opinions concerning the stratigraphy and age of the formations in the 
Catorce district, with quotations from the writings of various geolo- 
gists and travelers who have either visited the region or studied col- 
lections from it. The description of the fauna from the body of the 
work. in which sixty-five species and varieties of invertebrates are 
‘described, and nearly all of them are figured. Of these sixty-five 
forms, five are referred to the Brachiopoda, seventeen to the Lamelli- 
branchiats (including nine Aucelle), one to the Gastropoda, and 
forty-two to the Cephalopoda, of which thirty-eight are Ammonites. 
The fossils are not all from one horizon, but are distributed 
through the upper two members of a series, consisting of three groups, 
as follows, beginning at the base : 
1. Metamorphic argillaceous slates, without fossils. 
2. Alternating sandstones and marly and argillaceous shales, rich 
in fossils. 
3. Compact gray-ash colored limestones, more or less impregnated 
with silica, and containing nodules of black flint. The lower part of 
the group is argillaceous and has a shaly structure. Fossils rare. 
The only fossil found in the upper compact limestone is an imper- 
fect ammonite, supposed to be related to Schloenbachia inflata, but 
the calcareous and marly shales at the base of the upper group have 
yielded five species that are referred to Exogyra, Lucina, Phylloceros 
and two species of Hoplites. From a comparison of these forms with 
European species the authors conclude that the upper group probably 
represents the upper part of the lower Cretaceous, viz., the Aptian and 
the Albion. 
Two divisions are recognized in the middle group (No. 2), of 
which the upper one, composed of shales and marly sandstones carry- 
ing more or less lime, is the principal Aucella bed of the series. The 
fauna of Aucella recognized are all Russian species, as follows : Aucella 
bronnt, A. bronnt var. lata, A. pallost,, A. pallosi, var. plicata. A. pallosi 
var. tenutstriata, A. volgensis, A. fischeriana, A. piriformis and A. tere- 
bratuloides. ‘Vhese species which in Russia characterize various zones 
in the upper Jurassic and lower Cretaceous, are said to occur together 
in Mexico in beds, with a total thickness of not more than fifteen feet. 
Associated with them there are species of Lytoceras, Placenticeras, | ?] 
Pulchellia and Olcostephanus. 
The lower division of No. 2 consists of fine-grained sandstones and 
