0. C. Marsh — Discovery of Cretaceous Mammalia. 259 



One of the most interesting isolated teeth found is repre- 

 sented on Plate XI, figure 9. Several others with the same 

 structure of crown have been secured, but most of them are 

 much more worn. All are evidently deciduous, and they were 

 associated with the teeth of Didelphops. There can be little 

 doubt that they are the milk-teeth of the last premolar, and 

 probably pertain to that genus. The discovery of these 

 teeth is of special interest, as it connects the Cretaceous 

 forms with existing Marsupials. 



The only specimens described in this series of papers in 

 regard to the nature of which any reasonable doubt can be 

 suggested are the small Platacodon teeth the crowns of which 

 are figured in Part II, Plate VIII. In form, these are cer- 

 tainly like the crowns of some fish- teeth, but the best authorities 

 on the subject who have examined them do not consider them 

 such. They were found associated with characteristic mammal 

 teeth, some of which they closely resemble, especially various 

 small incisors, one of which entire is represented on Plate XI, 

 figure 7. A microscopic examination will determine the true 

 nature of the type. 



The specimens described and figured in the present article 

 all belong to the skull, the teeth being especially characteristic, 

 and best preserved. Associated with these, likewise, were 

 many parts of the skeleton, especially vertebrae, and bones of 

 the limbs and feet. Some of these specimens were illustrated 

 in Part 1, Plate V, and many others will be discussed in a later 

 communication. The bones of the skeleton now known con- 

 firm the conclusion derived from the teeth, that many genera 

 and species are represented in the collections made. Some of 

 the broader generalizations suggested by the preliminary study 

 of these remains are of special interest in connection with those 

 already presented, but cannot be given here. One or two 

 facts, however, may be mentioned. All the pelvic bones thus 

 far found have been separate. This is true not only of those 

 of young animals, but of some others apparently adult. The 

 bones of the feet, moreover, indicate that the specialization so 

 marked in the dentition of some of these early mammals was 

 not confined to the skull, but in one or more forms, at least, 

 had made equal progress in the extreriiities. 



For the rare and important material on which the present 

 communication is based, the writer is again mainly indebted to 

 his able assistant, Mr. J. B. Hatcher, whose field-work in verte- 

 brate paleontology has never been surpassed, and will be 

 appreciated more fully as the results of his explorations are 

 placed on record. 



