0. C. Marsh — Cretaceous Mammalia. 83 



uncommon, and the vertebrae of Ischyrosaurus occur with 

 them. The remains obtained place the reptilian nature of both 

 beyond question. Crocodiles of small size, turtles of fhe genus 

 Compsemys, and various fishes, mostly Ganoids, are abundant 

 in the same horizon. The invertebrate fossils indicate that the 

 deposits are of brackish, or fresh water origin.* 



The mammalian remains themselves also indicate to some 

 extent their horizon, and this is one of the interesting points 

 connected with the discovery. Many of them belong to the 

 group the writer has called the Allotheria, which contains 

 the Triassic Ti'iglyphtis, Tritylodon, and Microlestes, the 

 Jurassic Stereognathtis, Plagiaulax, and Bolodon, in Europe, 

 and Allodon and Ctenacodon, in America, as well as some later 

 forms. 



Most of the new genera show close affinities with the Triassic 

 and Jurassic forms, and one genus cannot at present be distin- 

 guished from Dryolestes. Another genus appears more like 

 an insectivore, with teeth of the same general form as Tupaia. 

 Besides these, there are several genera of small marsupials, 

 which, although quite distinct, seem to have near affinities with 

 some American Tertiary forms, or others still existing. 



Carnivores, Rodents, and Ungulates, appear to be entirely 

 wanting in this unique fauna. A still more surprising fact is 

 the absence of their probable ancestors, unless, indeed, the 

 insectivorous forms are entitled to this important position. 

 Many known facts point in this direction. 



As a whole, the mammals already found in these deposits 

 are very nearly what was expected from the Cretaceous, but 

 thus far, the older types seem to predominate. The Allotke?'ia 

 from this horizon appear to be distinct from the Marsupialia, 

 and some specimens secured point to the Monotremes as 

 possible allies. One genus, at least, of the new forms has a 

 free coracoid, as well as some other characters of Monotremes, 

 and it is possible that these features belong to the whole 

 group. These points will be discussed more fully later. 



The specimens briefly described below give some idea of 

 the rich mammalian fauna that lived during Cretaceous time, 

 and indicate what may be expected from future discoveries. 

 These and other remains from the same horizon will be fully 

 described and figured in a memoir on Mesozoic mammals, now 

 in preparation by the writer, under the auspices of the United 

 States Geological Survey. 



Q* Remains of a single bird were found at one locality in association with the 

 mammals. It was about as large as a pigeon, and had strong powers of flight, 

 It appears to be related to Apatornis, one of the toothed birds described by the 

 writer. It may be called Cirnolopteryx rarus. 



