CHIROPTERA. 373 



Portions of several other individuals were found by Mr. Wortmau in 

 the bad lands of the Big Horn Basin. 



Restoration. — From the preceding investigation we can form a general 

 idea of the form and proportions of the Mesonyx ossifragus. We can depict 

 an animal as large as a lai'ge-sized American black bear, with a long stout 

 tail, and a wide head as large as that of a grizzly bear. The fore limbs are 

 so much shorter than the hind limbs that the animal customarily sat on its 

 haunches when on land. In walking, its high rump and low withers, would 

 give it somewhat the figure of a huge rabbit. Its neck was about as long 

 as that of an average dog. Its tread was plantigrade, and its claws like those 

 of various rodents, intermediate between hoofs and claws. The animal, to 

 judge from its otter-like humerus, was a good swimmer, although there is 

 nothing specially adapted for aquatic life in the other bones of its limbs. 

 Its teeth, on the other hand, are of the simple construction of the mammals 

 which have a diet largely composed of fishes. We cannot but consider this 

 animal as one of the most singular which the Eocene period possessed. In 

 size it was not exceeded by any other flesh-eater of the period, but was 

 equaled by the Protopsalis tigrinm. 



CHIROPTERA. 



Species of this order were first detected in the Eocene formations of 

 France by Cuvier, who named a species from the gypsum (Upper Eocene) 

 Vespertilio parisiensis. In North America, Pi-ofessor Marsh has recorded 

 them from the Middle Eocene (Bridger), but whether they belong to existing 

 generic forms or not is yet unknown. The oldest North American species 

 is described below. It is from the Wind River region, which represents the 

 Lower Bridger. 



VESPERUGO Keys & Bias. 



Wirbelthiere Europas, 1810, p. 45. 



9 1 2 3 



I.-; C. -; Pm. — ;M. -. First and second superior tme molars 

 o 1 ^ — O O 



with two external Vs, and an internal heel, which supports a more or less 



elevated cusp. Inferior molars like those of Didelphys, with an anterior 



triangle of three cusps and a cuspidate heel. 



