RODENTIA ARVICOLINAE MYODES. 557 



however, as in Arvicola, and is, indeed, rather weaker than usual the claws no longer in 

 proportion. 



The second specimen referred to is probably of the same species. In it the fore feet have a 

 thumb claw rather longer and more linear than in Arvicola, but not as large as in Myodes. The 

 hind feet are short ; the soles sparingly hairy to the roots of the toes ; more pilose than in 

 Arvicola usually less than in Myodes ; the toes about two-thirds as long as the rest of the foot. 

 The proportions are as in Arvicola. Tbe tail is short ; densely hairy ; the longest hairs on the 

 terminal third, where the tail also appears to be depressed ; it is about one and a half times as 

 long as the hind foot. The feet and tail beneath are whitish ; tail above, brown, with a distinct 

 line of separation. 



The skull is broader than in Arvicola, though the exact proportions cannot be ascertained, 

 owing to its mutilated condition. The line of molars is long, and about equal to its distance 

 from the posterior base of the incisors. The nasal bones and nasal branches of intermaxillary are 

 equal, and scarcely pass the anterior line of the root of the zygoma. The cranium projects into 

 the inter-zygomatic cavity much more than in Arvicola, filling it, as in My odes, at the expense 

 mainly of the temporal portion of the fossa. The zygomatic arch is very high in the middle 

 portion, as in Myodes. The posterior extremity of the palate ends in two fossse, as in Arvicola, 

 not in a projecting shelf, as in Myodes and Hypudaeus. 



The lower jaw differs considerably from Arvicola in the greater size of the descending ramus, 

 and the width of its posterior edge. As in Hyodes, the root of the incisor passes along the inner 

 and lower edge of the borly of the jaw, and ends opposite the inner side of the root of the posterior 

 molar, instead of passing on under this molar to the posterior edge of the condyloid process, as 

 in Arvicola. The passage of the incisor along the inner edge of the body of the lower jaw gives 

 to the jaw a very great massiveness, as seen from below. The deep excavation between the 

 molars and the ascending ramus of Arvicola is wanting here. 



The incisors are very thick and strong. The upper have the inner edge rounded a little, but 

 the exterior is so strongly bevelled that nearly the entire surface is antero-external, instead of 

 anterior. There is a conspicuous, rather broad, groove near the external edge of the tooth. 

 Viewed laterally, the anterior two-thirds of the tooth is covered with enamel. The end of the 

 incisor is channelled deeply in its central portion. 



The molar teeth have exactly the structure of Myodes. The re-entrant angles are very deep, 

 extending mostly to the opposite side of the tooth. The anterior upper molar is composed of 

 five triangles an anterior and posterior, two internal and one external lateral though the 

 posterior triangle may be considered as an external lateral. The middle molar has four triangles, 

 an anterior, posterior, and one lateral on each side. The first and second triangles, however, 

 really extend across the tooth the inner being the only truly lateral one. The posterior 

 molar has four elongated triangles extending entirely across the tooth. 



The anterior lower molar has five triangles, of which the anterior and two posterior extend 

 entirely across the tooth. The first lateral is internal, and next to the anterior triangle ; the 

 second alternates with this, and is very small. The middle molar has four triangles, the ante 

 rior and two posterior going entirely across the tooth ; the fourth is external, next to the anterior 

 triangle, and hardly distinguishable. The posterior molar has, likewise, four prisms or triangles ; 

 it is a little smaller, but otherwise almost exactly like the middle one. The posterior molars of 

 both jaws are equally wide with the rest. 



The only difference in the teeth of this animal from Myodes is in having only four triangles 



