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944 



MONOGRAPnS OF NORTU AMERICAN KODKNTIA. 



SCIURAVUS NITIDUS Marsli. Sco antei, p. 03.->. 



SCIURAVUS UNDANS Miirsh. Sen fl«(<ii, p. 9S.'. , ,, • .;■'■.,,.„- 



SCIURAVUS PAEVIDENS Mursli. Koo aii(<i», p. 936. . ' ' - ; 



fSClURAVUS Lridy. Sw nii(i<>, p. 93(!. .. • 



Incertce sedis. ^' ' 



HELISCOMYS VETU8 Cope. See anUct, p. 936. 

 MYS0P8 FEATERNU8 Leidy. See a»i(fd, p. 937. 

 MYSOrS MINUTUS Leidy. See a«(fd, p. 937. 

 COLONYMYS CELEB Marsh. See aniei, p. 938. 

 TAXYMYS LUCARIS Marsh. See anIeA, p. 938. 

 TILL0MY8 SENEX Marsh. See aiitei, p. 93a 

 TILLOMYS PARVUS Marsh. See anteCL, p. 939. 



• CASTORID^. 



EUCASTOB TORTUS Leidy. See anted, p. 451. 

 STENEOFIBER NEBRASCENSI8 Leidy. See anh&, p. 463. 

 8TENE0FIBER PANSUS Cope. See anici, p. 455. 



ISCHYROMYID^. 



The family Ischyromyidm was recently proiwsed by Mr. E. R. Alston • for the recep- 

 tion of Dr. Lcidy's genus Ischyrcmys. Mr. Alston's diagnosis of the group, based ou 

 Dr. Loidy's figures and descriptions of his Ishchyromys typva, is as follows : — "Dentition 

 as in Sciuridai. Skull resembling CattoriikB, but with the infraorbital opening large, 

 a sagittal crest, no postorbital processes, palate broad, basioccipital keeled ".t 



Genus ISCHYROMYS Leidy. 



lachyramys Leidy, Proc. Acad. Nat. Sci. Fbila. 1850, 89. 



ISCHYROMYS TYPU8 Leidy. 



lachyromyi tijpiu Lkidy, Proc. Acad. Nat. Sci. Phila. 1856, 89; 1857, 89; Journ. Acad. Nat. Sci. Phila. '2d 

 ser. vii, 1869, 335, 405, pi. xxvl, figs. 1-C. 



About the size of a Muskrat [Fiber eibethicug). Form of the skull somowhnt 

 resembling that of the Beaver (Castor Jiber), but the interparietal region is greatly 

 narrowed, more even than in the Muskrat, with the frontal relatively wider. The infra- 

 orbital opening was apparently as large as in the Muskrat. Upper grinding teeth five, 

 "constructed after the plan of those of the Squirrel family". 



The lower grinders, four in number, also resemble those of the ScinridcB, and the 

 lower jaw fragments are described as resembling the corresponding portions of the jaw 

 of a Squirrel ; "but the impression of the masscter is comparatively feeble, and only 

 reaches as far forward as the position of the back part of the second molar tooth". ■ 



• Proc. Zoiil. Soc. Loud. 1870, 78. 



t Mr. Alston adds in a foot-note : — " It seems probable that Ptevdomj/n Cope [ = PnmdotomuB Copo] 

 (Proc. Amcr. Phil. Soo. 1872,467), from Ibo Kccene of North America, may belong to this family." 

 (Alston, /.c) 



