9o6 The American Naturalist. [October, 
species has been figured by Marsh (Amer. lour. Sci. Arts, 1889, p. 
336), under the name of Hadrosaurus brevueps. The lower jaw is 
figured as the upper, and is printed upside-down on the page. 
Agathaumid^. It is now evident that the genus Polyonax Cope 
(Triceratops Marsh) had elongate frontal horns, a relatively short one 
on the nasal bones, while Monoclonius Cope (Ceratops Marsh) has 
shorter horns on the frontals, and an elongate one on the nasals. The 
three codsified cervical vertebra which I described in 1876 (Proceed- 
ings Academy, Phila., October,) occupy a position below the posterior 
prolongation of the parietal bone in Monoclonius. This coossification 
is appropriate to the immovable condition of these vertebrae in the 
position mentioned. Marsh {Amer.Jour. Sci. Arts, 1890, Jan.) de- 
nies postacetabular pubes to the members of this family. I find them, 
however, in Monoclonius.— E. D. Cope, March 5, i8go. 
MINERALOGY AND PETROGRAPHY.^ 
Petrographical News. — In a most excellent paper, so full of 
information as to defy any attempt to do it justice in these notes, Lem- 
berg^ has given the results of his experiments on the stability of many 
rock-forming minerals when treated with water at high temperatures, 
and their power of resistance when subjected to the influence of solu- 
tions of various salts. The object of the experiments was to determine 
the cause of the widespread existence of certain minerals like leuciteand 
hauyne in effusive rocks, and their entire absence from intrusive rocks, 
and also to determine the conditions that gave rise to the properties of 
elaeolite and orthoclase on the one hand, and to nepheline and sani- 
dine on the other. The only conclusions that can be referred to in 
this place are those with reference to hauyne and leucite. The 
existence of the former mineral in effusive rocks is ascribed to the 
oxidizing effects of the oxygen of the atmosphere upon the sulphur 
compounds of these rocks, and the reactions set up between the solu- 
tions thus produced and the constituents of the rocks. The non- 
existence of this mineral in irruptive rocks is regarded as due to the 
protection from atmospheric oxygen which these rocks enjoyed as a 
1 Edited by Dr. W. S. Bayley, Colby University, WaterviUe, Me. 
2 7.eUs. d. deuUchen. geol. Gesell., XL., 1888, p. 625. 
