138 EXPLORING EXPEDITION FROM SANTA FE 



Formation and locality. The horizon at which the teeth of Ptyclwdiis 

 occur in the Cretaceous rocks of New Mexico is, according to my observations, very 

 clearly defined. It is below the middle of the series, generally within a hundred feet 

 of the yellow Lower Cretaceous leaf-bearing sandstones. 



The rock containing them is a sandy, ferruginous limestone, lying in thin bands 

 divided by layers of dark calcareous (often bituminous) shale. The associate fossils 

 are Lamna Texana, Gryphcca Pitclteri, Ostrca htgitlris, 0. uniformis, Inoceramus prollc- 

 maticus, I. f rat/His, Ammonites percarinatus, A. Macombii, Scapliitcs larrifonnis, &c. 



The Ostrea of which M. Marcou speaks as occurring with Pt. Wliipplei is not 0. 

 conf/esta, as he supposes, but 0. luyulris of Conrad. Tlie- place of 0. com/esta is a little 

 higher in the series, (injplifca Pitcheri is found a few feet below. 



Of all these species, specimens were obtained on the banks of the Canadian at 

 Galisteo, at the ford of the Chama, and at the Pagosa. 



ATHYRIS SUBTILITA, Hall, sp. 



Wherever we found Carboniferous rocks in the West, we were sure to meet with 

 this wide-spread fossil. On the Colorado, west of the San Francisco Mountains, at the 

 junction of the Grand and Green Rivers, in the Sierra la Plata, at Santa Fc', and at Pecos, 

 it is abundant. At all these places, the most common form of the Coal-Measures in the 

 valley of the Mississippi is most numerously represented ; there, as here, varying some- 

 what in size, apparently accordingly as it was well or ill fed. 



In the extreme upper Carboniferous or Permian beds, an Atliyris is common which 

 has sometimes been considered as distinct from those obtained below, for it is usually 

 larger and more ventricose than the prevailing type of Coal-Measure specimens. It 

 may possibly be a distinct species, but it is true that in many places in the Coal- 

 Measures A. sMilita is found, assuming precisely the same form and reaching an 

 equal size.. It will, therefore, be impossible to make two species of them until some 

 internal characters are found which can serve to distinguish them. 



SPIRIFER CAMERATUS, Morton. 



This shell is common in the limestone of the Carboniferous series at all points in 

 the route of our expedition where these rocks are exposed. Of the large number col- 

 lected in New Mexico and Utah, and a very much larger number examined, all exhibit 

 nearly the same character, the prevailing type as regards size and markings closely 

 resembling that figured by Professor Hall in Captain Stansbury's Report under the 

 name of S. triplicates. Specimens collected in Eastern Kansas and others obtained 

 from the banks of the Colorado are absolutely undistinguishable. The larger shell, 

 considered by Mr. Davidson identical with 8. striatus of Martin, is nowhere met with 

 in New Mexico or Utah. It is abundant in the mountain limestone of Illinois and 

 .Missouri, but I have never seen it from the Coal-Measures. Considering the marked 

 difference in form and position of these two shells, it is difficult to resist the conviction 

 that if the European palaeontologists could study what the}- regard as American 

 representatives of 8. str'talux in great numbers as the}- occur in place, they would con- 

 sider them as forming two distinct species. 



