620 



RODENTIA 



cusp-like projection on margin of central hollow, slightly above 

 level of alveolus. Lower incisor more slender than upper tooth, 

 its root extending to level of middle of m.„ its cross section essen- 

 tially like that of upper incisor, but greatest transverse diameter 

 in front of middle, and postero-external border distinctly flattened. 

 First upper molar with an anterior transverse loop and four 

 alternating closed triangles. The anterior loop somewhat 

 triangular in form, owing to the deep re-entrant angle at its 

 postero-internal border, the two closed triangles on lingual side 

 of tooth noticeably smaller than the others, their main axis 

 oblique instead of transverse, the salient angles tending to be 

 truncate at their extremites ; re-entrant angles four, all well 

 developed and regularly alternating, two on each side of tooth. 

 Second upper molar with crescentic anterior loop isolated by the 

 very deep first oviter re-entrant angle, a second loop essentially 

 like first loop of rii^, and two closed triangles like the posterior 

 pair in m^ but slightly smaller ; re-entrant angles three, all well 

 developed and regularly alternating, two outer and one inner. 

 Third upper molar with four loops extending completely across 

 crown, the first crescentic like that of m^, and similarly isolated 

 by a single deep inner re-entrant angle, the second slightly 

 narrower and bounded posteriorly by two exactly opposed 

 re-entrant angles, the third similar to second but bounded 

 posteriorly by a deep inner re-entrant angle and a very shallow 

 exactly opposed outer angle, the terminal loop with transverse 

 diameter slightly less than in the others, its posterior border 

 with a shallow but noticeable concavity on inner side ; re-entrant 

 angles five, the first (outer) extending across crown, the second 

 and third opposite and equal, the last two opposite and unequal, 

 the inner extending nearly across crown, the outer very shallow. 

 First lower molar with a narrow anterior loop thrown into a 

 projecting point in front by the presence of a broad concavity on 

 both outer and inner border ; closed triangles three, essentially 

 alike in form, but that on outer side noticeably smaller than the 

 others ; posterior loop similar to anterior loop of nr and vf but 

 narrower ; re-entrant angles five, all well developed and alter- 

 nating, two outer and three inner (in some specimens one or both 

 of the concavities on anterior loop might be counted as a small 

 additional re-entrant angle). Second lower molar with a posterior 

 loop like that of first, and four triangles, the first pair of which 

 are smaller than the second pair ; re-entrant aqgles four, all well 

 developed, two on each side. Third lower molar consisting 

 essentially of three tranverse loops isolated by the two re-entrant 

 angles extending across crown from inner side, but second loop 

 with postero-external border indented by a small but well 

 developed re-entrant angle which cuts off outer exti'emity of loop 

 as a closed triangle not quite equal in size to the outer closed 

 triangle of m^ and nr ; terminal loop similar in form to that of 

 the other mandibular teeth, but slightly larger and less narrowed. 



