192 PROCEEDINGS OF THE ACADExMY OF 



above, indistinctly paler below. Fur siiort, close, of so rich silky 

 lustre that in some lights an appreciable purplish or coppery iri- 

 descence is seen. General build of 2yineto7-um; rather stouter, 

 larger; nose to eye 0.50 ; to ear 1.05 ; to tail 4..33-4.45 ; tail verte- 

 bra 0.10 ; with hairs 0.80 ; height of ear in front 0.45 ; palm 0..33 ; 

 sole 0.66. 



Hah. Mexico. (Xalapa, De Oca, No. 3524, Mus. S. I., type of 

 the species ; Tuxpango, Sumichrast, No. 7006, Mus. S. I.) 



Obs. This peculiar field mouse, which may prove entirely dis- 

 tinct from pinetorum, is specially interesting in coming from a 

 region where the genus was long supposed to be not represented. 

 I have never seen any other Arvicola from south of the United 

 States, nor is there, to my knowledge, but a single one hitherto 

 described from so low a latitude, on this hemisphere at least. This 

 is Arvicola {Hemiotomys) mexicanus^ De Sauss., R, M. Z. 1861, 

 3, a species apparently allied to A. riparius. 



Genus VII. SYNAPTOMYS, Baird. 

 Stn. Synaptomys, Bd., M. N. A. 1857, 558, in text under Myodes, and p. xHv. 



Diag. Superior incisors grooved (unique in the subfamily). 

 Root of inferior incisor ending abruptly opposite last lower molar 

 (the root generally runs up to the condyle in Arvicolinae). Con- 

 struction of molars, and general cranial characters as in llyodes. 

 Palate ending as in typical Armcola. External characters in 

 general of an ordinary arvicoline style, but in the very long soft 

 full pelage, short heav}' head, and blunt muzzle, approaching tlie 

 Lemmings; nevertheless, ears equalling or overtopping the fur as 

 in Evotomys, and tail equally or exceeding the hind foot, as usual 

 in Arviicola. 



Obs. Foregoing are the essential characters of the most remark- 

 able genus of the subfamily, one singnlarl}' comlnning peculiari- 

 ties of several widely different arvicoline genera. It may be de- 

 fined in a -word as skull and teeth of Myode.^, in body of Arvicola, 

 with ears of Evotomys, and sui generis sulcation of upper incisors. 

 The genus was happily characterized in 1857, but upon such 

 miserably inadequate material,' that Prof Baird did not formally 



' ^^- 2"i5l' ^^^^^- ^- !' merely a rat-eaten bunch of fur, lacking head, tail, 

 and three of the feet, with a defective skull ; and No. 1368, skin with feet 

 and tail, but no head, and no skull. Locality unknown, supposed United 

 States. Eeceived from Wm. Cooper. 



