10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



the Clarkforkian of the Big Horn Basin. It is only a Httle smaller 

 than Torrejonian Didymictis haydenianus, but not to be compared 

 with D. microlestes or D. tenuis. Possibly the Almy form is a fore- 

 runner of one of the other miacid genera of the Eocene, but the tooth 

 in question is not too well preserved so that detailed comparison is 

 unwarranted. 



CONDYLARTHRA 



PHENACODONTIDAE 



ECTOCION RALSTONENSIS Granger, 1915 



Plate 2, figures i and 2 



Ectocion, though by no means as abundantly represented in number 

 of specimens as Phenacodus, has in the material comprising it cer- 

 tainly the best specimen in the Almy collection. The skull and jaws 

 (U.S.N.M. No. 20736) referred to Ectocion ralstonensis in general 

 lack only the right and posterior elements of the cranium and the 

 posterior portion of the right ramus of the mandible. The rostrum 

 and left side of the cranium and mandible are comparatively well 

 preserved, though fractured and slightly distorted. The teeth are for 

 the most part in excellent condition and only the upper incisors and 

 P^ and P- of the right side are missing from the skull. The lower 

 jaws have Pg-Ma preserved in both rami. An incomplete humerus and 

 ulna were found associated with the skull. There are, in addition 

 to this specimen, about 12 others consisting of jaw and maxillary 

 portions and isolated teeth referred to or tentatively identified as 

 E. ralstonensis in the Almy collection. 



In a lateral aspect the Ectocion ralstonensis skull reveals certain 

 details of interest regarding the foramina, so often not ascertainable 

 in Paleocene materials. The anterior opening of the infraorbital 

 foramen is directly above the anterior root of P^ and well forward 

 of the anterior margin of the orbit. Posteriorly this foramen opens 

 in the orbital cavity at the anterior apex of the large triangular-shaped 

 orbital plate of the maxilla. Superior and somewhat medial to the 

 posterior opening of the infraorbital foramen and separated from it 

 by a backward and medially extending ridge, which may coincide with 

 the sutural ridge of the maxilla, is an aperture believed to be a spheno- 

 palatine foramen. Above this and somewhat lateral to it is the lachry- 

 mal foramen, concealed in lateral view by the margin of the orbit. 



In the posterior portion of the orbital cavity, the optic foramen is 

 well forward — a little less than a centimeter — of the sphenoidal fis- 



