30 



NORTH AMERICAN FAUNA. 



[No. 38. 



foramen relatively small, the plate forming its outer wall moder- 

 ately broad (slightly narrower than diameter of foramen). Au- 

 dital bullse complete, depressed (relatively higher than in Scapanus) ; 

 auditory meatus short, scarcely developed. External pterygoid 

 region much inflated posteriorly, slightly inflated anteriorly. Mes- 

 opterygoid space broad, the sides gently concave. Palate mod- 

 erately elongate, terminating at a distance posterior to last molar 

 about equal to diameter of that tooth; posterior border of pal- 

 ate truncate, frequently with a median notch or spine. Anterior 

 palatine foramina small, oval to elliptical; first (anterior) pair of 

 posterior palatine foramina small (smaller than anterior palatine 

 foramina), round to oval; second (posterior) pair minute. Hori- 

 zontal ramus of mandible heavy, curved upward both at posterior 

 and anterior ends; coronoid process moderately elongate, triangular, 

 somewhat acute, directed slightly posteriorly; angle of mandible rela- 

 tively short, broad (broader than coronoid), and truncate; inferior 

 mandibular notch moderate, subcircular, relatively narrow and deep. 



Dental characters. — First upper incisor long and broad, convex in 

 front, flat posteriorly; second and third upper incisors lateral, simple, 

 conical, minute. Upper canine about two-thirds as large as first 

 incisor, simple. Upper premolars indistinctly cuspidate, the second 

 about twice the size of the first and about equal in size to canine (but 

 broader), the third about haK as large again as the second. Upper 

 molars W-shaped in transverse section, with an antero-internal 

 V-shaped cusplike shelf (not lobed) ; first and second molars subequal, 

 the third much smaller. 



First lower incisor small, elongate, conical; second lower incisor 

 about twice the size of the first, elongate, caniaelike, with an infero- 

 internal longitudinal groove; no persistent lower canine. Premolars 

 successively increasing in size posteriorly, somewhat simple, with a 

 shght tendency toward the development of a cingulum posteriorly. 

 Lower molars M -shaped in transverse section, the antero-internal cu^ 

 bilobed; molars successively decreasing in size posteriorly. Func- 

 tional dentition: i. f ; c. ^; pm. f ; m. |; total 36.* 



Keys to Species and Subspecies of Scalopus. 



I. KEY TO ADULT MALES. 



a.^ Geographic range east of Mississippi River, 



Total length more than 153 mm.; greatest length of skull more than 33 mm.; 

 breadth of skull across mastoids usually more than 17 mm. 

 c.^ Total length less than 190 mm.; length of hind foot less than 2 1.5 mm.; greatest 

 length of skull less than 37 mm.; breadth of skull across mastoids less than 

 19 mm Scalopus aquaticus aquaticus (p. 32). 



1 The actual dentition of Scalopus is: i. |; c. i ; pm. f ; m. §; total, 40. The third lower incisor and the 

 lower canine are nonpersistent and disappear before the animal is mature. 



