stanton.] COMPARISON WITH EUROPEAN FAUNA. 51 



usually been placed at the base of the Senonian. It is especially char- 

 acterized by the keeled Ammonites, such as those we have referred to 

 Mortoniceras and Prioncyclus and by certain forms of Inoceramus. 

 Several species are represented by identical or closely related American 

 forms, as follows: 



From the Colorado formation. From the Emscher Mergel. 



Inoceramus unibonatus. ) Represented by Inoceramus involutus. 



Inoceramus exogyroides. ) 



Inoceramus deformis. Inoceramus cuvieri. 



Baculites asper. Baculites incurvatus. 



Mortoniceras shoshonense. Mortoniceras vespertinum. 



On account of the occurrence of these forms and a few others in 

 Texas, Dr. Schliiter 1 has considered the beds (Austin limestone) con- 

 taining them the equivalent of the Emscher Mergel. 



It is interesting to compare these facts with the evidence furnished 

 by vertebrate fossils from the Colorado formation. I can not do this 

 better than by quoting the statements of Prof. E. D. Cope: 2 



The fanna of the deep sea epoch, the Niobrara, is the best known. Here the remains 

 of Pylhonomorpha constitutes the prevailing characteristic, while Elasmosaurus and 

 Polycotylus, with but few species, represent the numerous Sauropterigia of Europe. 

 Crocodiles were apparently wanting, while turtles and a peculiar group of Ptero- 

 sauria were only moderately abundant. The fish fauna was very rich and varied. 

 Here the Saurodontidce, like the molluscous family of the Budistw, appeared and as 

 soon disappeared, accompanied by the peculiar form Erisicthe and the family of 

 Stratodontidce. The genera of Mount Lebanon, Leptobrachelus and Spaniodoti 

 occur in this bed in Dakota, but the closest parallelism is exhibited with the Lower 

 Chalk or Turonian of western Europe. The general facies of the reptilian fauna 

 is that of the Lower Chalk, and there is little doubt that several genera are identi- 

 cal in the two continents, e. g., Elasmosaurus. The apparent peculiarity of the 

 Chalk in America is the abundance (four genera) of Pythonomorpha, with numerous 

 species, while but two genera have yet been found in Europe, and the presence of 

 birds with biconcave vertebrae and teeth. This interesting type, which was first dis- 

 covered by Seeley in the genus named by him Enaliomis, and afterwards found by 

 Marsh to have teeth, has been found at a lower horizon in England, the Upper Green- 

 sand. But in England, France, and Westphalia occur the genera of fishes above 

 mentioned, as, Porthenus, Iclithyodectcs, Saurodon, Sanrocephalus, Erisicthe, Empo, 

 Pachyrhizodus, Enchodus, Leptotrachelus, etc. This close relationship of the hori- 

 zons permits an identification, and it is the first instance that appears to me suscep- 

 tible of satisfactory demonstration. 



Again, on page 42 in u Eesume of Comparisons," he says: "Exact 

 identification of restricted divisions may be made in a few instances 

 only, such as the Turonian and the Niobrara." 



Sufficient evidence has been given to show that the invertebrate fauna 

 of the Colorado formation can not be divided into well defined sub- 

 faunas or zones corresponding to those that have been recognized in 

 Europe. It is true that certain types seem to be confined to the upper 

 part and others to the lower part of the formation, but some of the most 



1 Op. cit., p. 113, and Naturh. Ver. pr. Rheinl. Sitzungsb. Jahrg. 44, 1887, p. 47. 



2 Cope, E. D. : Cretaceous Vertebrata. U. S. Geol. Sur. Terr., vol. in, pp. 27, 28. 



