1<)1U.] Parainy.s; the Rodent Dentitiun. 327 



absent and the skull is markedly constricted back of thv orbits; tlu^ antero- 

 external slip of the niasseter muscle evidently had not yet excavated an 

 oblique antorbital depression for its reception, and Dr. Matthew informs the 

 writer that apparently the external slip of the masseter was limited anteriorly, 

 as it is in Aplodontia and the Hystricomorpha (primitive characters), and 

 on account of the downward direction of the small infraorbital foramen 

 it appears unlikely that the internal slip of the masseter had invaded that 

 foramen. 



The rest of the skeleton of Paramys differs in no important respect (so 

 far as figured by Cope) from the generalized Sciuromorph type. It has 

 the characteristic ilium and limb bones. Its astragalus is also of the Rodent 

 type: with wide trochlea, sharp keels, no astragalar foramen, a short broad 

 neck, and a wide convex head, which is flattened antero-j^osteriorly and 

 twisted on the neck so that its long axis points oblicjuely backward and 

 inward. Other generalized characters, observed in American Museum 

 material of Paramys by Dr. Matthew, include the very long and large tail, 

 entei)icondylar foramen in humerus, third trochanter on femur, toes 5-5, 

 separate scaphoid, lunar and centrale, separate radius and ulna, tibia and 

 fibula. 



Cheek teeth of Paramys. — The molars are roundly triangular in form, 

 consisting of a blunt inner cusp from which two diverging ridges pass to 

 the para- and metacones; the anterior cingulum is either not prominent 

 (P. delicatissimus, Cope, 1884, pi. xxiv a, fig. la), or more prominent and 

 connected with the parastyle; but this anterior crest, which became pro- 

 nounced even in the Oligocene Prosciurus vetustus Matthew (1903, p. 213) 

 was not so high and prominent in Paramys as it is in Arctomys. The crown 

 of the lower molars is divided into two parts, the anterior corresponding to 

 the trigonid, the posterior to the talonid. The antero-internal cusp is ele- 

 vated; it is possibly the metaconid; the talonid is broadly basined, with well 

 developed hypo- and entoconids. 



" Trituberculy" vs. the "Prcm,olar Analogy" Theory in the Rodentia. — 

 The dentition of Paramys thus seems to a})proach the tritubercular-tuber- 

 culosectorial type; but Dr. Wortman (1903, pp. 217-218), in criticising the 

 theory of trituberculy, takes the view that the principal cusp in the lower 

 molar of Paramys is not antero-external like the "protoconid" of normal 

 molars, but antero-internal, as it is in the premolar (p^), which is assuming 

 the molar form. As Dr. Wortman believes that molars have generally 

 passed through the stages later revealed in the premolars, he infers that 

 since the true "protoconid" in the lower premolars of Paramys is evidently 

 on the inner side, it is so also in the molars. 



This conclusion, if true, tends to remove the Rodentia very far from the 



