ilO [OcTOBEn, 



pale brown hair ; carpus aiicl tarsus hairy beneath. Tail well clothed with short 

 hair above and tipt with dark brown, beneath pale brown. 



Length 4-7 ; tail -8 ; head 1*2 ; ears -l? ; fore leg -8 ; hind leg 1'4. 



The dentition is precisely like that of the preceding, the A. pinetorum. 



I know nothing of the habits of this animal, but Conclude from its large eyes, 

 Ihat its life is not subterranean. 



The next genus which I shall examine is Hesperomys ; of this I have two new 

 species to describe, one from the North and one from the South, and as an ap- 

 pendage, shall add the Mus Leconteiof Bachman, which is a Reithrodon, and 

 neither a Mus nor a Hesperomys. 



Those American animals which were formerly arranged in the genus Mus, 

 have, from a more attentive examination, been removed to this. For a long time 

 naturalists hesitated where to place them; hence, we sometimes find them called 

 Arvicolae. Mr. Waterhouse finally gave them the name which they now bear. 

 Whether the illustrious author intended by this name to indicate their nocturnal 

 habits, or their western habitat, in either case it is perfectly appropriate. It 

 may well be doubted whether there is a single species of Mus really indigenous 

 to America. There is but one instance which makes me hesitate to assert this 

 positively. In Georgia there is a rat, inhabiting the middle parts of the State, 

 which Dr. Bachman considers as a variety of the Mus Rattus, from which, how- 

 ever, it appears to me to differ very considerably. How it could be imported 

 from abroad and only found in the interior of the country, and there not in cities 

 and among human habitations, I cannot conceive. Why has it not extended 

 everywhere as well as in the more southern States ? and why has nothing re- 

 sembling it ever bef?n described in Europe, whence we have undoubtedly received 

 the Mus Rattus? It may have been brought from Africa or some tropical region, 

 and therefore not able to bear any colder climate than that of Georgia or South 

 Carolina. 



The molars of Hesperomys vary from those of Mus in the following particulars : 

 They are proportionally longer and smaller. In Mus they have each three trans- 

 verse striae-tubercles ; in Hesperomys, the series of teeth present a double row of 

 tubercles not standing perfectly opposite each other, but more or less alternating, 

 and separated in the middle by a deep longitudinal furrow meandering among 

 them ; the inner ones of these tubercles in the upper jaw and the outer ones in 

 The lower, seeming to be formed by a reduplication in the sides of the teeth. All 

 the molars have some alternating indentations or folds of the enamel. The first 

 has 2 internally and 1 externally, the rest having one on each side, except H. 

 ieucopus, whirh in the second superior molar has 2 on each side, one of the exte- 

 rior being smaller. On the two first teeth of the upper jaw there is a small false 

 tubercle at the mouth of each of the indentations. The indentations and the tu- 

 bercles of the hindmost tooth, both above and below, become early obliterated. 

 In the lower jaw the number of tubercles are similar to what we find in the 

 upper, that is to say the first tooth has 5 tubercles, the second 4, and the third 3. 

 This is the structure of the dentition when the teeth are not altered by age and 

 long use ; when, however, the tubercles become ground down, the plicated figures, 

 which formerly were of a determinate and invariable form, become changed, and 

 finally vanish entirely, and the surface of the tooth becomes plain. When the 

 teeth of a Mus are abraded, there are formed on the surface simple oblique fur- 

 rows across their crowns. I begin with the largest of the genus. 



1. Hesperomys palustris. Pilis cinereis, supra saturatioribus, extremitati- 

 bus supernis fuscis et nigris, abdominalibus cinereo-albis. Auribus parvis intus 

 et extus pilosis. 



Ilah. In Georgia? et Carolinrc oryzaceis. Mus palustris Harlan, Silliman's 

 Journ., xxxi., 385. Wagner, 1. c. p. 543. Arvicola oryzivora Aud. and Bach., 

 Quadrupeds of N. A., vol. iii. p. 214. 



Hair cinereous, above darker, tipt with brown and mixed with longer and 

 blacker hairs, which are more numerous on the back, so as to make that part of 

 the body much darker, beneath tipt with grey. Nose rather pointed; ears small, 

 nearly round, clothed both inwardly and outwardly with short hair. Feet 



I 



