460 Annals of the Carnegie Museum. 



Tlie Phalanges. — The phalanges of the type (No. 918) are pro- 

 portionally shorter than they are in the recent camel and llama, and 

 are less symmetrical. The proximal ends of the first row of phalanges 

 have the concave articulations for the metapodials much deeper than 

 those of the llama and the recent camel. The grooves for the meta- 

 podial keels are deep and there is a nodular tuberosity on either side of 

 the groove on each phalanx which is well illustrated in PI. VIII, Fig. 

 3. In the camel and the llama the metapodial groove is shallow and 

 the rugosity for the attachment of the pad extends well forward. 

 Distally the trochlea is deeper and more oblique than in the recent 

 camels, and external keels do not extend as high up on the pos- 

 terior face of the shaft. The phalanges of the second row have a de- 

 cided ridge separating the articular facets articulating with the proxi- 

 mal phalanx. This ridge is obsolete in the recent genera. As in 

 Pocbrotheriitm the second row of phalanges are proportionally longer 

 than in the recent Tylopoda. The phalanges of the first and second 

 row in O. lo)igipes do not seem to have changed any in character from 

 those oi Poebrotheriiim}'^ Cope says that "the phalanges (in Proca- 

 inelus occidentalism " only differ from those of the llama in the greater 

 prominence of the proximal ligamentous insertions and the rather 

 more slender shafts." If the illustration is correct in Plate LXXIV 

 in the publication just referred to, it is obvious that the proximal 

 phalanx in P. occidentalis is like that of O. longipes and without the 

 plantar rugosity for the attachment of the pad. The comparative 

 length of the bone, however, is more like that of the llama than is the 

 corresponding bone in O. longipes. 



The Unguals. — The ungual phalanges in O. longipes are compara- 

 tively short, laterally compressed, pointed and high ; they have not 

 changed in shape from those of Po'ebrotheriiiin while in comparative 

 length there seems to be considerable difference, the former genus 

 having the unguals more reduced than the latter. The phalanges in 

 O. longipes, as a whole, seem to retain characters seen in the early 

 Oligocene forms, while other Loup Fork genera '"^ have unmistakably 

 taken on these tylopod characters, such as the rugosity on the plantar 

 face for the pad and the general flattening of the median phalanx. 



^^Joiirn. Morph., Vol. V, No. I, p. 37, 189 1. 



'<"U. S. Geogr. S.," Vol. IV, Part II, p. 337, 1877. 



1^ Specimens in the American Museum studied by the writer. 



