338 0. a Marsh— Principal Characters of the Brontotherida. 



The limbs of the Broniotheridm were intermediate in proportion 

 between those of the Elephant and the Ehinoceros. The scapula 

 is large, with a prominent spine and small coracoid process. 

 The humerus is stout, and its great tuberosity extends above 

 the head. The radial crest is prominent, and the entire 

 distal end is occupied by the articulation. The olecranon cav- 

 ity is shallow, and the condylar ridge similar to that of the Ele- 

 phant, but not continued so far up the shaft. The radius and 

 ulna are separate. The ulna has its olecranon portion much 

 compressed. Its distal end is much smaller than in Rhinoceros^ 

 and has no articular face for the lunar. The radius is stout, 

 and its distal end expanded. The carpal bones fonn interlock- 

 ing series. They are shorter than in E/mwceros, and support 

 four well developed toes of nearly equal size. (Plate XIII, 

 figure 2.) The metacarpal bones are shorter than those of Ehi- 

 noceros, the first phalanges longer, and the second series shorter. 

 All the toes had "navicular" sesamoid bones, similar to that 

 on the coronary bone of the horse. The ungual phalanges are 

 short and tubercular, as in the Dinoceraia and Prohoscidea. 



The pelvis is much expanded transversely. The femur has a 

 small third trochanter, and its head a deep pit for the round liga- 

 ment. At the distal end, the anterior articular surface is narrow, 

 and the two edges are of nearly equal prominence, as in the Tapir. 

 The patella is elongate, and has a strong vertical keel on its 

 articular face. The tibia is stout, and has a distinct spina 

 The fibula is separate and entire, but quite slender. The cal- 

 caneum is much elongated. The astragalus is shorter than in 

 the Rhinoceros, and the superior groove more oblique. The 

 cuboid face is larger than in Rhinoceros. The navicular has its 

 distal facets subequal. There were three toes of nearly equal 

 size in the pes, the first and fifth being entirely wanting. (Plate 

 XII, figure 1.) None of the bones of the skeleton are hollow. 



There appear to be four well marked genera in the Bronio- 

 theridae^ now known, which may be distinguished as follows : 



1. Menodus Pomel.* {Titanotherium Leidy, 1852.) 



Dentition =Incisors~ ; canines—; premolars — ; molars—. 



Diastema behind upper canines. Basal ridge on inner side of 

 upper premolars not continuous. Nasals short. A postorbital 

 process. Third trochanter rudimentarv or wanting. Type M. 

 Proutii. 



2. Megacerops Leidy. {Megaceratops Cope), {Symhorodon Cope 

 in part.) ^ 

 Dentition =r Incisors — ; canines — ; premolars-^ ; molars—. 



* Bib. Univ. de Geneve, x, p. 75, Jan., 1849. 



