Weights of two males were 80 and 82, and of a female 66 grams.
Oryzomys palustris aquaticus differs from O. p. peragrus in having a rich cinnamon, reddish color and the interorbital region constricted to less than 14.7 per cent of the greatest length of the skull. O. p. peragrus is ochraceous and grayish. The least width of its interorbital region is more than 14.5 per cent of the greatest length of the skull. Individuals studied from the Sierra de Tamaulipas are typical aquaticus. Of those from Altamira, one has the color as in aquaticus, but the color of the other two resembles that of peragrus; nevertheless, all of the mentioned specimens are here assigned to aquaticus.
Records of occurrence.—Specimens examined, 4: Sierra de Tamaulipas, 10 mi. W, 2 mi. S Piedra, 1200 ft., 1; 6 mi. N, 6 mi. W Altamira, 2; 5 mi. N, 5 mi. W Altamira, 1.
Additional records: Camargo (Goldman, 1918:40); Matamoros (ibid.); near Cd. Tampico (Ingles, 1958:395).
Oryzomys palustris peragrus Merriam
1901. Oryzomys mexicanus peragrus Merriam, Proc. Washington Acad. Sci., 3:283, July 26, type from Río Verde, San Luis Potosí.
1918. Oryzomys couesi peragrus, Goldman, N. Amer. Fauna, 43:39, September 23.
1960. Oryzomys palustris peragrus, Hall, The Southwestern Nat., 5:173, November 1.
Distribution in Tamaulipas.—Western part of state, along Sierra Madre Oriental.