DAPLODONTIDvE— DISCUSSION OF AFP1NITIK8. 



553 



coming between Caatorida nnd Sciuru/a, with close relntiunHliip on (lie one 

 liaiul with Castor, and on tlic otiicr with Arctomya. 



My views of tiie |N>8ition in the Rodent series, nnd relative mnk in the 

 scale, of the Ilaplodont type rest upon an examination of the wiiole structure 

 of the animal. I do not find that any one has hitherto examined — at any rate, 

 given an account of — the viscera, or even the skeleton, excepting the skull and 

 leg-bones ; our knowledge having thus far rested \\\m\\ these |)ortions of the 

 bony frame-work, the teeth, and the external characters. I nin, consequently, 

 enabled to add many new particulars to substantiate the position here taken. 

 Detailed descriptions are ofTcicd beyond under head of the species ; here I 

 shall simply advert to some of the leading ])oints involved. 



The skull of HaplodoHtid(t is strongly and unmistakably Sciuromorphic, 

 not only in its general structure, but in many ultimate details. In fact, it 

 resembles in superficial ospect the skull of certain typical Sciurines more 

 closely than some of these resemble each other. For example, no one who 

 compares the skull of Haplodon with that of Arctomya can fail to be struck, 

 as Dr. Peters was, with their close general resemblance. In comparison with 

 Sciurua, or even with such a Marmot-like form as Cynomys, the skull of Arc- 

 tomya is seen to be much more massive, much more depressed, broader behind, 

 and with a straightness and mutual perpendicularity of various planes, all of 

 which features wonld require little exaggeration to match those of Haplodon, 

 Even the shape of the angle of the mandible, peculiar to Haplodon, is really 

 approached in Arctomya, where further twisting of the already oblique plate 

 of the descending ramus would bring it into the nearly horizontal plane 

 which it occupies in Haplodon. The most prominent diiference is the totiil 

 absence of postorbital processes in Haplodon, and their full development in 

 Arctomya as in other Sciurvla. It may be fairly questioned, however, whether 

 the presence of these processes is more than a character of th" family Sciu- 

 ridce itself; for they are lacking* in the three other families referable i 

 Sciuromorpha. The preponderance of recent genera and species of Sciuridt 

 may have unconsciously led us to attach too great importance to this feature. 

 Obviously, the fact that the family Sciurida at present contains many genera, 

 while the other three Sciuromorph families have but one genus apiece, is no 

 argument for the making of postorbital processes a requisite for any scries of 

 Sciurines of higher value than a family. The argument is the other way, in 



* Mr. Alston calls tbom " obsolote " iu Ammalurida. 



