PHENACODUS. 475 



portion of the shaft. Three succeeding segments of the sternum are pre- 

 served, which increase in width posteriorly. The last (fourth) is longer than 

 wide, and flat, with truncate extremities. As compared with the sternum 

 of the Phenacodus primcevus, the praesternum of the P. vortmani, is much less 

 compressed posterior to the costal articulations, and the peduncles of the 

 latter are more prominent. The fourth sternal segment in the P. primoevus 

 is shorter and wider. I find no trace of clavicle in this species. 



Measurements of ribs and sternum, 



M. 



/ from liead to tubercle 006 



[ transverse) of tubercle 00o5 



Widthsof fourtli rib^, ( of shaft near tubercle 0065 



(^ anteroposterior at proximal fourth 0025 



Length of 12th or 13th rib 109 



Diameter of 12th or 13th rib at middle 0045 



Length of presternum 0515 



Length to posterior base of rib facet 023 



Depth at anterior base of rib facet 009 



Depth at posterior extremity 008 



Width at posterior extremity 008 



/ c anterior 0065 



\ ^Tl Tift VAf^ft / y\ 



Diameter second or third segments \ posterior Oil 



( an teroposterior 022 



, f anterior 0015 



Diameters fourth or fifth segment 5 ''''"sverse^ posterior 013 



( anteroposterior 0195 



The scajnila is like that of P. primcevus reduced in size. The oval 

 glenoid cavity with anterior acumination separated by a shallow groove 

 from a short subconic posteriorly turned coracoid process, is the same in both 

 species. Both the scapulae are somewhat mutilated, so that while the pro- 

 tuberance of the anterior edge above the neck is evident, it is not possible 

 to know whether it is as much extended as in P. primcevus. One portion lost 

 in that species is present in the specimen of P. vortmani; the acromial process. 

 As in the AmUypoda and Proboscidea, the spine of the scapula is recurved, 

 forming a prominent shelf along its proximal portion ; while the proximal 

 extremity is extended forwards and downwards in a considerable acromion. 

 As its extremity is broken off the length cannot be ascertained. This 

 scapula resembles that of the Linocerata and Proboscidea, with an acromion 

 added. This gives it very much the character of that of some rodents, as 

 Sciurus. 



