438 Annals of the Carnegie Museum. 



being the antero-posterior. It is placed nearl)'^ as far back as in the 

 llama, and is closed behind by a bony bridge as in the latter genus. 

 The inclosing of the orbit seems to have been completely accom- 

 plished in the genus Pro/oiNc/yx while in Poebrotheriiiui the orbit is still 

 open.^ The skull has the upper contour somewhat similar to that of 

 the recent camel, especially the frontals and parietals. 



The sagittal crest is low, but well defined, and is nearly in line with 

 the frontals, as in Procamelus occidentalis. '' Slight crushing has taken 

 place in the posterior region of the skull in the type, which in PI. IV, 

 Fig. I gives a slightly more depressed appearance to the supra-occip 

 ital region, than would otherwise be the case. There are cavities 

 below the nasals and above premolars ^ and ^. These cavities seem 

 quite a constant feature among the known Loup Fork Camelidje. The 

 zygomatic arch is slender and the malar process deeply notched to 

 receive the corresponding wedge-shaped process of the squamosal. In 

 the antero-superior region of the orbit there is a deep notch similar to 

 that in Po'cbrotherium. This notch is also present in the recent genera, 

 though not so deep. The crano-facial axis is straight. The occipital 

 condyles seem to be subject to some variation ; in some cases they are 

 rather high and narrow, while in others they are rounded, similar to 

 those oS. Po'cbrotherium. In the type the condyles are high and narrow ; 

 inferiorly they are separated by a groove which extends across the 

 accessory facets on the basi-occipitals, as in the camel and the llama. 

 In Pocbrotheriuin this groove is entirely wanting, as is also the acces- 

 sory surface for the inferior arch of the atlas. The supra-occipitals in 

 O. lougipcs are high with prominent lambdoidal crests. The parietals 

 are comparatively long, thus forming a longer, but somewhat narrower, 

 brain case, than is seen in the llama, and more like that of the camel. 

 In Oxydactyltis the sagittal crest is thin and much higher than in the 

 recent genera, and also differs from the latter in its almost rectangular 

 contact with the elevated inion. in the camel the superior part of 

 the supra-occipitals forms a broad and rather flat triangular surface 

 where they meet the sagittal crest, which is low and short. In general 

 appearance this region of the cranium of O. longipes more closely re- 

 sembles that of the camel than the llama. 



The zygomatic process of the squamosal is short in comparison with 

 that of the camel and the llama, but as in the latter genera, is ta{)ered 



^ Bull. Am. Mus. Nat. Hist., Vol. X, pp. 114, 115, 189S. 



*" U. S. Geogr. S.," Vol. IV, Part 2, Plate LXXVII, 1877, Lieut. G. M. Wheeler. 



