CYCLOPIDIUS 241 



Skeleton: Scott (1890B, pp. 355-356) described part of the manus as follows (freely trans- 

 lated from the German) : 



Of the hand I have been able to study the pyramid, magnum, Mc. II, and the proximal ends of Mc. Ill, 

 IV, and V. The pyramid does not differ importantly from that of Oreodon; the magnum, on the contrary, is 

 shifted still more to the radial side and lies almost completely under half of the scaphoid; it does not, however, 

 bend around the lunar in a crescent, as it does in Merychyus and to a still greater degree in Merycochoerus; on 

 the radial side there is a very small facet for Mc. II. 



The metacarpals, in so far as can be judged from the present material, are not especially long or strong. 

 Mc. II has a decidedly prominent articular surface for the trapezoid, and, since this bone rises higher than 

 Mc. Ill, it has a small lateral connection with the magnum. The hand is likewise of the unreduced type, as is 

 common in the oreodons, and in consequence of this it differs essentially from that of Merychyus. Mc. Ill is 

 not much stronger than Mc. II, the difference being less than in Merycoidodon; the head has an apparently small 

 facet for the magnum and sends out a strong process to the hamatum. The inferior side of this process and the 

 ulnar side of the diaphysis are excavated for the head of Mc. IV. Mc. IV appears to be similar in construction to 

 Mc. III. Mc. V is somewhat slimmer than Mc. II; the head shows a small, very slightly concave facet for the 

 hamatum. What is especially noteworthy in the hand is the similar development of all the metacarpals, that is, 

 the middle toes but slightly surpass the lateral ones in size and strength. This apparent isodactyly confirms the sup- 

 position that Leftauchenia had developed an aquatic mode of life. 



Genus CYCLOPIDIUS Cope 1878 

 Table 1 3 



Original Reference: Descriptions of new Vertebrata from the Upper Tertiary formations of the West. 

 Proc. Amer. Philos. Soc, XVII, p. 221. 



Synonyms: Brachymeryx Cope 1878; Pithechtes Cope 1878; Sespia Stock 1930. 



Genotype: Cyclofidius simus Cope. 



Genoholotype: Cat. No. 8116 A.M.N.H., skull, with zygoma and about half of brain case on right side 

 longitudinally sheared away. 



Distinguishing Characters: Skull small, brachycephalic (indices 0.71-0.72) ; facial vacuities 

 enormous; premaxillaries very small and rotated; face much shortened; nasals, frontals, and maxil- 

 laries much reduced, with frontal taking no major part in cranial roof, as it does in the other genera; 

 orbits large and very much elevated; malar very deep, long, and heavy; basicranial region fore- 

 shortened, with development of enormous bulls and with auditory meatus large, highly placed, and 

 posteriorly directed; postglenoid process compound; chin more vertical than average in merycoido- 

 donts; symphysis coossified; dentition hypsodont; I 2 : 3 . 



Discussion: Cope originally described upper incisors for this genus, but he later (1884B, 

 p. 504) concluded that they were "early shed," so that his formula was "I °> C i» Pm 4> M \. n 

 It is now well verified that there are two superior incisors normal to this genus, with usually three 

 inferior, perhaps two in some forms (Cope said only two in the genoholotype), but we may find 

 specimens without any inferior incisors, especially as these teeth are so small that they are seldom 

 preserved and perhaps in some instances, as Cope said, were "early shed." Other types of ungulates 

 have shown similar specialization in the loss of upper incisors and in the subprismatic molar shape. 



The deciduous third upper premolar is longer and more complex than its successor, and the 

 DP 4 is like M 1 . In the lower series the three anterior milk premolars are similar to their successors, 

 but DP 4 is trilobate. 



The genus is undoubtedly a near relative of Leptauchenia and seems to possess, in an exagger- 

 ated form, the various peculiarities of the latter. The nasal vacuities are larger; the frontals are 

 shorter and form less of the cranial roof; the zygomata are much heavier and more widespread; the 

 nasal bones are much narrower, expanding at their sutural union with the maxillaries; the external 

 auditory meatus is situated somewhat more posteriorly; the basicranial and facial regions are more 

 foreshortened; the skull is heavier and more brachycephalic; the rami have become more robust 



