286 



SCIENCE 



[N. 8. Vol. XXXVI. No. 922 



The order may be defined and distinguished 

 from the Rodentia as follows: 



LAGOMOBPHA 



Incisors, four above (functional), six in youiig 

 individuals. 



Functional premolars, three above and two be- 

 low. 



Dental formula If, Pm|, Mf or f rarely 5. 



Palate broad, distance between upper tooth rows 

 much greater than the lower. 



Upper cheek-teeth much wider than the lower. 



Surface of glenoid fossa divided into two parts, an 

 anterior ridge and a posterior pocket, thus limit- 

 ing the jaws to a lateral motion only in chewing. 



Cheek-tooth row in plane with ascending ramus of 

 lower jaw. 



Cfficum with spiral fold. 



Elbow joint modified, not permitting of rotary 

 motion of the forearm. 



Fibula fused with tibia, distally, and articulating 

 with calcaneum. 



EODENTIA 



Incisors, two above, never more than two in young 



individuals. 

 Functional premolars never more than one above 



and one below. 



Dental formula I ^ , Pm — z — ( 



A^3 



Palate progressively narrow, distance between 

 upper tooth rows less than the lower. 



Upper and lower cheek-teeth about equal in width. 



Surface of glenoid fossa broad and continuous, 

 permitting both anteroposterior and lateral mo- 

 tion of the jaws in chewing. 



Cheek-tooth row lying inside plane of ascending 

 ramus of lower jaw. 



Cascum without spiral fold. 



Elbow joint primitive, permitting free rotary mo- 

 tion of the forearm. 



Fibula fused or free, distally, but never articu- 

 lating with the calcaneum. 



Other difFerenees than those given above 

 might be added to the list, but these, if prop- 

 erly weighed, seem to suffice. True, some of 

 the characters here given seem trivial, as, for 

 instance, the difference in numbers of the 

 upper incisor teeth. In some groups of mam- 

 mals this character is not regarded as of more 

 than specific value, but in the groups under 



discussion, in the light of other important 

 modifications, it denotes a fundamental differ- 

 ence in the mechanical construction of the 

 dentary system, and thus assumes a far greater 

 importance. 



As understood by the writer, both the Lago- 

 morphs and the Rodents represent very an- 

 cient orders, whose origin dates so far back in 

 time, and about which so little is known owing 

 to the lack of fossil remains, that their real re- 

 lationships to other placentals and to each other 

 are at present very uncertain. However, from 

 present evidence the former seem not to 

 stand any closer to the Rodentia than to some 

 other of the great groups of the mammalia. 

 In this connection it is interesting to note 

 some apparently early acquired characters in 

 which the Lagomorphs have paralleled the 

 higher ungulates.^ The more important of 

 these are: (1) modifications of the dental sys- 

 tem, such as (a) broad palate with distance 

 between the upper tooth rows much greater 

 than the lower (ruminant), (b) upper molari- 

 form teeth wider than the lower, (c) manner 

 of chewing on one side at a time with a lateral 

 motion of the jaws; (2) modifications of the 

 limbs and feet, (a) radius lying anteriorly 

 to the ulna proximally, with articular face 

 extending the full width of the humerus, (b) 

 humerus with well-developed intertrochlear 

 ridge, (c) fibula articulating strongly with the 

 anterior face of the calcaneum (artiodactyl) ; 

 (3) dorso-lumbar vertebrae 19 (artiodactyl, 

 rodent). 



These characters, while perhaps in no way 

 denoting relationship to the higher ungulates, 

 nevertheless indicate an advance in general 

 development beyond the Rodentia which mark 

 the later as the more primitive order. The 

 existing differences in the brain and reproduc- 

 tive organs seem also to favor this conclusion. 



The present article is intended simply to 

 present the principal grounds for establishing 

 a new order for the Lagomorphs, without at- 

 tempting a full discussion of the subject. 

 James W. Gidley 



' Some of these characters were pointed out by 

 Cope in 1883, Report U. S. Geological Survey, 

 on Terr., F. V. Haden, Vol. III., p. 813. 



