of the Genus Stenomylus. 



303 



is of moderate length and spout-like in form. The angle of 

 the mandible is not produced into the upward hook-like pro- 

 cess so common among the tylopods but shows simply a slight 

 projection (see fig. 6) at that point. The coronoid process is 

 short and slender, being slightly recurved. The articular con- 

 dyle is broad and slightly concave, the postglenoid facet being 

 large and resembling that of the llama. 



The following measurements give the proportions of the 

 skull : 





Length in- 



Length 



Orbit 



Width 



Width 







Specimen 



cisor to occ. 



premolar 2- 



weight by 



across 



across 



Age 



Sex 





condyle 



molar 3 



width 



orbits 



molars 2 







S. hitchcocki 

 type 



166 



60.5 



27x26-5 







barely 

 mature 



$ 



S. hitchcocki 

 2019 



179 



58 



24x28 



67 



37 



old 



$ 



S. hitchcocki 

 1090 



191 



67 



28x29 



68 





mature 



$ 



S. hitchcocki 

 2009 





33 p 2 - 4 









milk 





S. crassijies 



211 



78 









mature 





S. gracilis 





80 



27 x 26 



95 



57 



mature 





Age. — The series of adult skulls fall into two classes irre- 

 spective of the amount of wear of the teeth, namely smaller, 

 lighter ones, which I should interpret as female ; and larger, 

 heavier ones, which would be .males. Aside from these char- 

 acters of relative proportion I have found no distinctive sex 

 characters. As all the associated skeletons must have been 

 accumulated at one time, and births presumably took place in 

 the spring, such individuals as show differences in age must 

 have been a year apart. On this basis, the youngest, which 

 have the entire milk dentition and the first molar just showing, 

 would be one year old ; while the next set, in which the third 

 molar is just up, would be two years old, at which time they 

 have reached nearly full size, as shown by such a specimen as 

 the type. How long they lived would be difficult to estimate, 

 but every indication points to very rapid wear of the teeth ; 

 so that live or six years seem to me to represent the probable 

 length of life of the older individuals studied. 



Dentition. — The dental formula is i.fc.ip.|-m.-| 



3 — 22 

 ~~ 2"2" 



U, 



which is the full and primitive set. The upper incisors are 

 simple chisel-shaped teeth, entirely unreduced and crowded 

 into a full series. The upper canine is laterally compressed, 

 making it into a subincisif jrm tooth, which stands a little 

 apart from the incisors, however. Behind the canine there is 



