9 



Some of the vertebrae display stout triangular neural spines; on the 

 lumbars the posterior zygapophyses are embraced laterally by the 

 grooved correspondents of the succeeding vertebra. Some of the caudal 

 vertebrae are long, slender and without neural arch, indicating that this 

 genus, like Mesonyx, had a long slender tail. 



Affinities. Having described the available parts of this form, it re- 

 mains to consider its place in the zoological system. The structure of 

 the dentition of the upper jaw, with the mode of articulation of the 

 mandible remove it from such orders as Eodentia and Edentata; the 

 only remaining ones with which it is necessary to compare it are the 

 Perissodactyla, Proboscidia and Carnivora. As many of the diagnostic 

 bones are wanting, it is necessary to rely on collateral and empirical 

 indications of relationship. From tapiroid types the development of 

 the tympanic region distinguishes it. From Proboscidians the slender 

 feet and reduced ulna, as well as the longitudinal crests of the teeth 

 separate it. It then remains to compare it with Perissodactyles of the 

 types which possess strong canine teeth. In points of resemblance to 

 these we have the flat claws and separate scaphoid and lunar bones, 

 nevertheless the greater number indicate truer affinity to the Carnivora. 

 Such are the external transverse glenoid cavity, the teeth with longi- 

 tudinal crests, the slender digits, the well developed tympanic bone ; 

 confirmatory are the large canine teeth, the incomplete orbit, aiid the 

 projecting inner condyle of the humerus. The form of the claws is not 

 absolutely incompatible with the same order, as it is approximated by 

 some of the Seals. 



Among Carnivora, the feet are like both dogs and bears. The very 

 prominent postglenoid ridge, and the narrow tympanic chamber* are 

 decided points of resemblance to the bears, but the cavu'm tympani is 

 even less expanded than in those animals. The characters of dentition 

 are more like those of the Hycenodontidce and Mesonyx than any other 

 group, and even the remarkable incisor-like inferior canines are ap- 

 proximated by the anteriorly directed canines of Hytxnodon leptorliynchus, 

 Laiz. et Par. 



As a summary, it may then be concluded that the j;enus SynoflotJterium 

 is a Carnivore, presenting a number of points of resemblance to the 

 bears, and to the extinct Hywnodons; but that its distinct scaphoid 

 and lunar bones, and flat claws ally it to other fofms of Mammalia, show- 

 ing it to be a more generalized type of the order than either of 

 the above. The peculiar approach of the lower canines is a special 

 modification for peculiar habits, which I suspect to have been the 

 devouring of the turtles which so abounded on land and in the waters 

 of the same period. The slender symphysis could most 'readily be in- 

 troduced into the shell, while the lateral pressure of the upper 

 canines with the lower, would be well adapted for breaking the bony 

 covering of those reptiles.f It is not unlikely that this genus, Mcwny.r, 



* See Prof. Flower's Osteology of Mammalia on this point. 

 t See Proceed. Amer. Plulos. Soc. 1872, p. 484. 



