403 [October, 



Hair above dark plumbeous tipt with bro\rn and black, beneath dark slate- 

 colored mixed with brown, particularly on the breast, the upper and under sides 

 of the body being nearly alike. Head large and blunt ; ears rounded, longer than 

 the fur, outwardly hairy, inwardly only so on the upper margin ; antitragus large, 

 semicircular ; whiskers black and grey, shorter than the head. Feet covered with 

 shining grey hair; thumb tubercle with a compressed, sharp, hooked nail. Tail 

 slender, thinly covered with short hair, above mixed brown and black, beneath 

 brownish grey. 



Length in. 5'5 ; head 1'3; ears '8; fore leg !! ; hind leg 1*5 ; tail 1'4. 



4. Arvicola RiPARius. Brevis et robustus, antice quam postice latior. Supra 

 fuscus, per dorsum subnigricans, subtus cinereus. Capite obtuso, auribus sub 

 pilis occultis, antitrago magno. Cauda pilis brevibus bene vestita, supra nigra, 

 subtus pallidissime fusca. 



Hah. In paludibus provinciarum borealium. (Phila., Mr. Ord.) A. riparius 

 Ord., Journ. Acad. Nat. Sci., vol. iv. p. 305. A. pennsylvanica. Richardson, 

 Fauna boreali americana, vol. i. p. 120. Idem Audubon and Bachman Quad- 

 rupeds of N. America, vol. i. p. 341. Id. Wagner's SuppL, vol. iii. p. .^88. Id. 

 Schinz, vol ii.p. 247. A. hirsutus Dekay, Zoology of New York, vol. i. p. 86. 



Body short and robust, broader before than behind. Hair dark lead color, 

 above tipt with brown, darker along the back, beneath with grey. Head short, 

 larger and blunter than in any other species ; ears short, rounded, hairy both 

 within and without, entirely concealed under the fur; antitragus large, semicir- 

 cular, nearly closing the auditory aperture ; legs and feet brovv^n, the latter 

 covered with short, shining hair ; thumb tubercle, with a short compressed sharp 

 nail. Tail well covered with hair, above dusky, beneath very pale brown. 



Length 6 inches ; head 1*4 ; breadth of head 1*8 ; ears .4 ; fore leg 1 in. ; hind 

 leg 1-8; tail 1-3. 



Swims and dives well ; is found peculiarly on the marshes of those rivers 

 where the Zizania aquatica grows. As there is a considerable difference in the 

 t^eth of some of these animals, I have, whenever it was in my power, pointed 

 out their peculiarities. With the exception of one species which will be men- 

 tioned hereafter, they differ much from those of Europe. Unfortunately I have 

 not been able to obtain crania of many of those here described, otherwise certain 

 distinctive marks might have been obtained, which would have rendered their 

 determination much more easy. 



System of De7ititio7i. In the upper jaw the first molar is composed of 5 tri- 

 angles, 1 anterior, 2 exterior and 2 interior; the second of 4 triangles, 1 anterior, 

 2 exterior and 1 interior, with a small posterior, rounded lobe ; the third of 5 tri- 

 angles, 1 anterior, 2 exterior very small, 2 interior, and ends in a trcffle, the ex- 

 terior lobe of which is nearly obliterated, leaving a plane space from the end of 

 the tooth to the posterior triangle. 



From this arrangement it results, that the line of teeth in the upper jaw' con- 

 sists externally of 9 salient and 9 re-entering angles, the two last of each small, 

 and internally of 10 salient and 8 re-entering angles, exclusive of the interior 

 emargination of the treffle. 



In the lower jaw the first molar commences with a treffle, then follow C tri- 

 angles, 2 exterior, 3 interior and 1 posterior ; the second of 5 triangles, 2 exterior, 

 2 interior and 1 posterior ; the third of 3 triangles, 1 anterior, 1 intermediate 

 and 1 posterior: and the line of teeth is formed externally of 11 salient angles, 

 including the exterior lobe of the treffle, and 9 re-entering angles, including the 

 concavity of the side of the treffle, and internally of 11 salient and 11 re-entering 

 angles, including the lobe and the emargination of the treffle. 



5. Arvicola Oneida. Supra niger, pilis sparsis fuscis intermixtus, pluribus 

 super caput et ad genas, lateribus et abdomine saturate plumbeis, hujus pi- 

 lorum extremitatibus fuscis, illorum pallidioribus et cinereis. Auribus subpilis 

 occultis. Cauda supra nigra, subtus nigrante. 



Hab. A Noveboraco ad Pennsylvaniam. Arv. Oneida Dekay, Zoology of 

 New York, 1. c. p. 88. 



Hair short and close, not shining; on the back black, with scattering brown 



