484 



U. 8. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



This species is very remarkable for the combination it presents in the skull of the characteristics 

 of Hesperomys and Sigmodon, as might have been expected from the external form. The teeth are 

 very similar to Hesperomys, except, perhaps, that the salient angles of the upper molars are more 

 opposite, and the lower molars rather broader. The zygomata are parallel in general direction, 

 as in Hesperomys, instead of diverging posteriorly, as in Sigmodon. There is, however, the short 

 and broad muzzle of Sigmodon ; the deep emargination of the anterior extremity of the zygo- 

 matic arch as viewed from above ; the sharp compressed ridge bounding the upper border of the 

 orbit, starting at the narrowest portion of the inter-orbital space, and continued less distinctly 

 to the occiput. The notch at the posterior extremity of the bony palate differs from either, ID 

 being more posterior ; in fact, behind the posterior molar, by half the length of the molar 

 series, instead of being nearly on a line with the posterior molars. There is a fossa in the bony 

 palate behind, and a little within the posterior upper molar, as in Sigmodon, but the two of 

 opposite sides are not separated by an elongated compressed azygos process, as in Sigmodon. 



Other remarks on the subgeneric affinities of this species will be found under the head oi' 

 Hesperomys, at the head of this article. 



This species was first described by Harlan, in 1837, from a specimen said to have been caught 

 near Salem, New Jersey. If this locality be correct, and the animal the same, it will indicate 

 a much wider range along the coast than at present known to naturalists. 



The generic name is borrowed from its habits, as given by Audubon and Bachman, o:' 

 frequenting the rice fields, and doing considerable damage to the crops. 



The insertion of the species in the genus Arvicola, by Audubon and Bachman, is a mistake, 

 all its affinities being with Hesperomys. 



List of specimens. 



