74 MICROTIN^ 



and similar though weaker fringes are developed along tlie 

 margins of the hands. The tail is very long, about two-thirds 

 of the head and body length, laterally compressed, covered 

 with small scales, and most inconspicuously clothed over its 

 general surface with short stiff hairs ; but along the mid-dorsal 

 and mid-ventral borders the hair is longer and denser, com- 

 pletely hiding the skin, and producing behind a very short stiff 

 terminal pencil. The mammary formula is 1 — 2 = 6. Perineal 

 glands, secreting a powerful musk, are well developed. 



Apart from the primitive characters above mentioned the 

 skull is highly specialized; it is very large and massive, and in 

 general form and structure closely resembles the skull of the 

 more highly specialized species of Microtus. The interorbital 

 region is greatly constricted. The temporal ridges in adults 

 are relatively closely approximated throughout, fusing anteriorly 

 to produce a sharply salient, median interorbital crest. The 

 squamosals are large, relatively closely approximated both 

 anteriorly and posteriorly, with their post-orbital crests strongly 

 developed and extensive, forming the square shoulders of the 

 braincase. The rostrum is long and slender, to accommodate the 

 large incisors. The pterygoid fossae are deep, their floors dis- 

 tinctly dorsal to the ventral surface of the basisphenoid. 



Neofiber is another North American genus of great interest. 

 It is represented by a single species known to occur only in eastern 

 and central Florida. Like Ondatra it is specialized, though less 

 profoundly, for aquatic life; but in its dental characters it has 

 progressed much further than that genus. Neofiber is a very 

 large vole, although considerably smaller than Ondatra. The 

 fur, eyes, and ears are substantially as in the latter, but the 

 long contour hairs produce a sort of dorsal keel in the neighbour- 

 hood of the rump. The hands and feet are moderately large, 

 with naked palms and soles ; the hind claws are distinctly longer 

 and stouter than those of the fingers; the foot is less evidently 

 twisted than in Ondatra, and there are five plantar tubercles, the 

 postero-external one being suppressed and the postero-internal 

 pad rounded. The " swimming -fringes " on the borders of the 

 feet and toes are much weaker and less conspicuous than in 

 Ondatra, but that along the outer border of the hand is better 

 developed than in that genus. The tail is long, as in Ondatra, 

 but is of quite different form, being terete and fully clothed with 

 long stiff hairs. The mammary formula is 1 — 2 = 6. Flank 

 glands are conspicuously developed in both sexes, even in the 

 young. 



The skull is essentially like that of Ondatra, but is character- 

 ized by its great fronto-palatal depth, evenly convex antero- 

 posterior dorsal contour, and conspicuously salient post-orbital 

 squamosal processes. The temporal ridges are more widely 

 separated, the intertemporal portions of the parietal and inter- 

 parietal being relatively broad. The palate is essentially as in 



