522 



REPORT OF STATE GEOLOGIST. 



SYNAPTOMYS COOl'EKI STONEI (Uhonds). 

 THE STONE LEMMING MOUSE. 



JSynaptomys stonei Rhoads, Amer. Nat., Vol. 27, p. 53, 1893. 

 Synaptomys cooperi Evermann and Butler, Proc. Ind. Acad. 



Sci. for 1893, p. 126. 

 Synaptomys cooperi stonei Rhoads, Proc. Acad. Nat. Sci. Phil. 



1897, pp. 305, 392. Hahn, Proc. U. S. Nat. Mus., Vol. 32, 



p. 460', 1907. 



Diagnostic characters.- — Color above, brownish gray; form 

 squat and heavy ; tail less than one inch ; upper incisors grooved. 



Description. — The shade of color varies considerably. In in- 

 dividuals in summer pelage the color is decidedly rusty, the short 

 fur of the back being all tipped with ferruginous, which the long 

 overfur partly conceals. The winter specimens usually are paler, 

 the tips of the short fur being cinnamon or fulvous. The sides 

 are paler and the belly is pale slate color, with the plumbeous bases 

 of the hairs showing through more or less. Throat and underlip 

 of some individuals white, of others slate. 



The status of the various names that have been given to differ- 

 ent forms of Synaptomys, and the relationships of these forms has 

 not been satisfactorily determined. The history of some of these 

 names, together with reasons for adopting stonei as the name for 

 the Indiana form of the lemming mouse, has been given by the au- 

 thor (Proc. TI. S. Nat. Mus., Vol. 32, pp. 460-461), and he has seen 

 no reason to change his conclusions. Since that time he has col- 

 lected lemming mice on the Missouri River in South Dakota, which 

 are apparently the form gossi and differ markedly from the Indi- 

 ana specimens in being much larger and clumsier, with larger and 

 heavier skull. 



M easurernenis. — Ten specimens from Mitchell averaged 113.2 

 mm. (4 8/16 in.) in total length; tail, 18.5 mm. (12/16 in.) ; hind 

 foot. 17.2 mm. (11/16 in.) ; ear fi'om cj'own, 9 irnn. (6/16 in.). 

 Three from AVolcottville. Lagi-nnj^c^ County, avei-age, total length, 

 114.3 mm.; tail, 20 mm.; iiind foot, 1(5.3 mm. 



SkvJl and hclh.-'Vlm skull of 'the Indiana Synaptomys is inter- 

 medijilc in siz(^ between that of the typical species (cooperi) from 

 the cMst and that of the si)ecies gossi from the plains region. The 

 general features of the skull are given under the diagnosis of the 

 genus. Average measurements of ten skulls from Mitchell are: 

 Greatest length, 26 mm.; ])alatilar l(>ngth, 12 mm.; greatest width 

 of braincase, 12 nun. ; depth of brai?icase ovci- bullae, 9.6 mm ; l(Migth 

 of molar loot h row, (i.S mm. 



