210 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Cams and other Carnivora there is a considerable lateral exposure of 

 the mastoid; in Can is it faces parth' backward. In the marsupials 

 and in some Irsectivora the exposure is entireh^ posterior, the 

 squamosal (lambdoidal) crests continuing the occipital crest downward 

 on each side and the mastoid exposure lying within them. 



The lower jaw is unusuallj- deep, with long loose symph3\sis extend- 

 ing back to a point beneath the anterior border of the third premolar. 

 In the posterior portion it is quite like the long-jawed Carnivora in 

 form, presenting none of the peculiarities of angle and coronoid seen 

 in Insectivora, Chiroptera, and Marsupialia. The anterior and poste- 

 rior mental foramina have the normal carnivore position, the former 

 l)eneath the diastema between P^ and Pg, the latter beneath P^. In 

 certain Insectivora the posterior mental foramen is beneath My. This 

 unusual character appears to be of importance in indicating rela- 

 tionship. 



Com/xirisotu with Jlysenodon. — The dentition of Hyfenodon is very 



prQtocone liypoconc 



p.rotoconc 



^^ ^a me /{* ^, )»-^ ^^ 



piracone t mehcone mebistyle 

 deuterocone 



protocone 

 Fig. 6.— Evou'TioN oi- tuk Upper Carnassial in Creodonta and Carnivora. Series .1, Hy.eno- 



DONTID.E (,SE<()NI) Mol.AU, RIGHT SIDE); ^l, DeLTATHERIUM; ,1-', SiNOPA; A'', Tritemxodon; A*, 



Pterudon; A'\ Hy.enodon. Serie.s Ji, Canid.« (fovrth premoi ar, rkjht side); li\ Pal.eonictis; 

 If-, DiDYMicTis; B'-', Daphcenus; B-i, Canis. The carnassial of Felis, not included i.v this 



SERIES, IS MUCH MORE LIKE THE HY^ENODON CARNASSIAL. 



[Published in advanco, ))y oourtesy of Prof. H. F. Osboni, from liis forthconiiiig memoir upon 



Trituberouly,] 



clearly derivable from that of Sinopa^ through Pterodon and Tritein- 

 nodun^ as Scott and Wortman have pointed out in various publications. 

 The accompanying liguros, drawn from models made ))y the writer, 

 illustrate these stages in the evolution of the specialized carna.ssial of 

 Kycenodon. The changes correspond in upper and lower teeth, and 

 are exactly analogous to the development of the carnassial in the true 

 Carnivora. In the upper teeth the two series begin in teeth of widely 

 different form and end in ver}' similar teeth, furnishing one of the 

 most striking (examples known of true convergent adaptation, in that 

 it results in the production of similar form from originally dissimilar 



