E. L. Troxell — American Bothriodonts. 333 



In the large number of skulls in the Marsh Collection 

 the genus Elomeryx shows the greatest variation, includ- 

 ing a specimen of E. hrachystylus Osborn and Wortman 

 (Cat. No. 10387, Y. P. M.). The canine has lengths of 

 from 10 mm. to 45 mm. One has a choice of calling this 

 a sex feature or of considering the specimens as widely 

 separated and distinct ; the former seems more probably 

 correct. The postcanine diastema varies from 20 mm. 

 to 35 mm. and its length bears no relation to the size of 

 the canine. The second premolars may vary from 9.5 

 to 13.5 mm. in width, the lengths are constantly around 

 16 or 17 mm. As already shown, the third premolars 

 have various lengths and mdths and many differences 

 in the nature of the triangular crown. 



Other eccentricities are shown in the table above. A 

 rather important feature, characteristic of neither of 

 these specimens, is the position of the cingulum running 

 up the side of the hypocone ; in the types just compared, 

 the cingulum either ends abruptly (E. armatus), or is 

 continuous around the base of the cone. There is great 

 diversity to be seen in the form of the styles, especially 

 the metastyle, and in the depth of the notches separating 

 them. 



Minor skull variations affect the width, pointedness 

 and curvature of the postgienoid processes, the form and 

 separation of the occipital condyles, the groove on the 

 ventral side and other cranial features. 



The extreme position of the posterior nares set far 

 behind the molars, the elongation of the cranial portion 

 of the skull, and the development of the wide shelf of bone 

 immediately behind the last molar seem to depend on old 

 age ; but we have to look to the immature animal for the 

 greatly inflated auditory bullae. 



In only one instance in the collection are there found 

 the complete lower jaws belonging to a skull. This is 

 a slender animal with canines less than 10 mm. in their 

 longest diameter, the symphysis being weak and the whole 

 structure light. This specimen (Cat. No. 10391, Y. P. 

 M. ) has a particular value in the study of the wear of the 

 teeth, for we find the upper P* quite unworn, while the 

 P^ and M^ on either side have lost nearly all the enamel 

 from the crowns. The consequence is that in the lower 

 jaw Ml and the posterior half of P4 are worn down in a 

 deep transverse groove. 



The teeth are so short crowned and so little protected 



