Thirteen specimens of frogs collected in the summers of 1960 and 1961 in the Mexican states of Durango and Sinaloa represent a heretofore unnamed species. The specimens have been deposited in the Museum of Natural History of the University of Kansas (KU) and in the Museum of Michigan State University (MSU). The species may be named and described as follows:
Holotype.—KU 63326 (Fig. 1); obtained eight miles west of El Palmito, Sinaloa, approximately 6100 feet, on 23 June 1961; original field number, 2354 of Robert G. Webb.
Paratypes.—A total of 12 specimens: KU 63327-33, same data as holotype, 23-25 June 1961; MSU 4085-88, two miles north of Pueblo Nuevo, Durango, approximately 6000 feet elevation, 24 July 1960; MSU 4089, one half mile west of Revolcaderos, Durango, approximately 6600 feet, 29 July 1961.
Diagnosis.—A species of Tomodactylus possessing the following combination of characters: (1) tips of two outer fingers truncate, about twice width of narrowest part of digit; (2) tympanum small, less than one half diameter of eye; (3) ventral surfaces smooth; (4) contrasting marbled pattern on back and top of head, and (5) venter whitish, lacking dark marks.
Description of holotype.—Adult male; snout-vent length, 31.5 (measurements are in millimeters and were taken by means of dial calipers reading to one tenth of a millimeter); width of head, 11.2; length of head, 10.3; horizontal diameter of eye, 3.1, and of tympanum, 1.2; distance from eye to nostril, 3.8; internarial width, 2.9; interorbital width, 4.1; width of eyelid, 2.5; lumbar gland (left side), 7.0 x 2.6; distance from axilla to groin, 15.2; tibial length, 12.7; length of foot, 13.1.
Head slightly wider than body; tip of snout rounded, slightly truncate; canthus rounded; tympanum small, less than one half diameter of eye; tympanum having posterior margin ill-defined, separated from eye by distance about equal to diameter of tympanum; diameter of eye slightly less than distance from eye to nostril; width of eyelid about two thirds interorbital width; paratoid gland indistinct; lumbar glands high, separated from insertion of leg by about one millimeter; back and sides of body having low, scarcely elevated pustules; top of head, limbs and venter smooth; few low, whitish pustules below and behind tympanum, and low on sides of body; posterior surface of thighs and anal region pustulate; one pair of whitish postanal spots; ventral disc attached near insertion of legs, lacking conspicuous transverse fold; skin loose on throat, chest and abdomen.