1861.] OF GUATEMALAN MAMMALS. 283 



further, and from this the foot is covered with short, adpressed, sil- 

 very hairs, grey on the foot and white on the toes. 



The general colouring is remarkable, and unlike that of any other 

 species of Neotoma. All the upper parts are of a bright rufous 

 colour, and all the under parts pure white, the line of separation 

 being very clear and distinct. The fur of the back is mixed with 

 black hairs, giving that part a much darker colour than the sides of 

 the body, where these hairs are less abundant. Fur of the outer 

 surface of the fore and hind legs strongly tinged with dusky, inner 

 surface of the fore legs whitish, of the hinder ones dusky grey. On 

 nearly all parts of the body the fur is bicoloured, dusky at its roots 

 for two-thirds of its length ; on the upper parts the dusky colour 

 becomes almost black, and on the under much paler. From the 

 chin to the space between the fore legs is an elongated patch of fur 

 which is pure white from root to tip, just as in Hesperomys atro- 

 gularis. The tail is deep dusky above, paler below ; claws white. 



In the outline of the grinding-surfaces of the molar teeth, this 

 species differs from all others at present described. Without en- 

 tering into a minute description of these teeth, of which it is difficult 

 to give a clear idea without figures, it may be stated that they have 

 somewhat the same arrangement of cusps as those of N. cinerea of 

 Baird, saving that in the present species the anterior cusp or prism 

 of the first tooth in the lower jaw is in a position decidedly outside 

 the line of the cusps of the other teeth. The exposed ends of what 

 I have termed the prisms of these teeth constitute their grinding- 

 surface, which, instead of having an angular outline as in N. cinerea, 

 present, as in those of N. floridana, fa series of transverse ovoid or 

 loop-like figures ; but these loops iii the present species are much 

 narrower in an antero-posterior direction than in any other species, 

 owing to the folds of enamel entering more deeply and broadly into 



the sides of the tooth. 



// /// 



Length of the head and body 6 6 



of the head 1 9 



of the ears 8 



of the fore-arm 1 3 



of the fore foot and claws 8 



of the tibia 1 5 



of the tarsus and toes 1 3 



of tail 6 



Breadth of the ears 8 



of the hind feet at the root of the 



inner toe 3 



Length of the skull from the front of the nasal 



bone to the occipital crest 1 8 



Breadth across the zygomatic arch 11 



Length of tlie nasal bones 8 



from the point of the upper incisor to 



the crown of the first molar G 



of the molar series 4 



