Notes on Tlioviomys bulbirorus. 115 



No. Se.r. Date. Length. Tail. HinrI foot. 



Ill $ May 5, 1890 260 74 37 



III S' May 12, 1890 280 73 41 



ii? (^ May 12, 1890 255 67 38 



The longest hind foot among thirteen specimens of T. bottle 

 from Nicasio, Marin county, California, is 32 mm. ; shortest, 

 28 mm. ; average. 29.7 mm. 



Thomomijs bulhivorus differs from T. bnttcV. so greatly in color, 

 as well as in size, that a detailed comparison of the two animals 

 is scarcely necessary. In T. boitx the ])revailing tint throughout 

 is wood-brown, more or less mixed with russet dorsally- and 

 blackening aljout the moutli, muzzle, and cheek-i)ouches. The 

 latter are here, as in T. bidbivorus, lined with white ; the area 

 between, however, is usually dusky, sometimes more or less 

 marked with white, Ijut never, or at least very exceptionally, 

 wholly white. 



The skull of TJioiiionv]-^ baihirorus, in addition to its very much 

 greater size, differs from that of T. boltfv. in many details of 

 structure. The occipital portion is In'oader and flatter (ratio of 

 height from inferior lip of foramen magum to mastoid width 50 

 in bidbivorus, 54 in bottle) and the fronto-palatal depth proj^or- 

 tionally greater. The dorsal aspect shows no decided points of 

 difference, though in T. bidbivorus all ridges and muscular at- 

 tachments are more strongly accentuated. Ventrally, however, 

 important differences at once present themselves. That surface 

 of the exoccipital which appears on the ventral as2)ect of the 

 skull immediately laterad of the condyle is in T. bidbivorus oc- 

 cupied by a deep groove running obliquely to the axis of the 

 skull, wliile in 7'. boU;e the surface is almost flat. The basi- 

 occi[)ital is much broader in proportioii to its length in bnlbivorus 

 than in bntt;e ; the audital bullae of the former ai'e much flatter and 

 less inflated than in the latter. Tlie form of the pterygoids differs 

 markedly in the two species, those of T. bidbivorus being much 

 the larger and strongly concave internally with hamulars con- 

 verging at the tijjs, while in T. botUe these bones are flat, with 

 hamulars divergent posteriorly. Both foramen magnum and 

 external nares are broader in proportion to their height in 

 T. bidbivorus than in T. bottx. Except in size, the mandibles 

 and teeth of the two species show no distinctive characters. 



The following table of cranial measurements and ratios of 

 Thjjmomys bidbivorus and 7\ bottm will serve to illustrate some of 

 these differences in greater detail. 



