255 



f GerUlliis leonurus, Eafixesque, Am. Mooth. Mag. 1818, 44(). 



Desmarest, Mamni. ii, 1822, 322 (compiled from Eafiaesque). 



Lesson, Man. i, 1827, 2.57 (compiled from Eafinesqne). 

 ? Diptis leonurus, Fischer, Syu. 1829, 339 (compiled from Eafinesque). 

 f GerUllus megalops, Eafinesque, Am. Month. Mag. 1818, 446. 



Desmarest, Mamm. ii, 1822, 322 (compiled from Eafinesque). 



Lesson, Man. i, 1827, 257 (compiled from Eafiuesque). 

 f Dipiis megalops, Fischer, Syn. 1829, 340 (compiled from Eafinesque). 

 ? Gerbillus maa'ourus, Eafinesque. 

 f GerUllus iracTiyurus, Eafinesque. 

 Meriones microcephalus, Harlan, Proc. Zool. Soc. Lond. vii, 1839, 1. 



ScHiNZ, Syu. Mamm. ii, 1845, 92 (compiled from Harlan). 

 Meiiones acadicns, Dawson, Edinb. N. Philos. Journ. iii, 1856, 2, pi. 1. 

 Canada Bat, Pennant, Quad, ii, , 172. 



Labrador Eat, Pennant, Hist. Quad. 1781, 435, No. 295 ; Arct. Zool. i, 1784, 132, No. 63. 

 Jumping Mouse of Canada, Davies, I. c. 

 Labrador or Jumping Mouse, GODMAN, I. c. 

 Canadian Jerboa, Shaw, /. c. 

 Labradore Jerboa, TuRTON, I. c. 

 Canadian and Labrador Gerbil, Griffith, I. c. 



Deer Mouse, DeKay, I. c. . 



Gerbille du Canada, Desmarest, I. c. 

 Merione du Canada, Lesson, /. c. 



Gerbille soricine, de la bale d'Hudson, queue de lion, et aux yeux noirs, Less., i!. e. 

 Canadlsche, Labradorisehe, Kleinlopfige Hiipfmaus, Schinz, I. c. 



Description. 



Cranial and dental cJiaracters. — In comparison with tlie murine forms 

 with whicli it has been associated, this animal presents many strong 

 peculiarities of the skull and teeth. Among these may be enumerated 

 the presence of an additional tooth in the upper molar series, causing an 

 inequality in the formulae of the two jaws; the size and shape of the 

 anteorbital foramen, with its supplementary foramen or nick just beneath; 

 the extension of the malar bone up the slender styloid zygomatic por- 

 tion of the maxillary till it sutnres with the lachrymal, and the slender- 

 uess and depression of the rest of the zygomatic arch ; the shortness 

 and transverse position of the bullae auditorice ; the position of the mas- 

 illo-palatine suture ; expansion of the posterior nares, «&c. The skull, as 

 a whole, is shorter for its width, though the zygomata are even more 

 nearly parallel ; it is also deeper for its other dimensions, with a greater 

 degree of convexity, both lengthwise and crosswise, of the superior con- 

 tour. IsTevertheless, its general superficial resemblance, aside from 

 details, to that of Miis proper, is evident. Compared with that of Mus 

 musculus^ wliich is of about the same size, we see in each species the 

 same general shape and delicate papery condition, without strong angu- 

 larity, as well as many close coincidences in detail, indicating that the 

 murine affinities of the family are with tj'pical Mus, Mesperomys, &c., 

 and not with the arvicoline group of Murida', in which the skull is nota- 

 bly heavier, more massive, and angular. 



As to the general shape of the skull, there is little to be added to the 

 foregoing, except such points as, being equally applicable to the familiar 

 Mus musculus, need not be recapitulated ; we may therefore at once 

 proceed to details. 



The anteorbital foramen, which transmits the masseter in this instance, 

 and which constitutes a prime peculiarity of the skull, is of great size 

 and obliquely oval in shape. Instead of being circumscribed by a plate 

 of bone, as in Muridfe, it is defined externally by a very slender styloid 

 process of the maxillary, which is strengthened by the upward exten- 

 sion of the malar, applied as a splint along its whole li?ugth. Below this 

 main foramen there is another much smaller one, which transmits the 



