LEMMUS 191 



the outer infolds are much deeper and the outer salient angles 

 much larger than those of the inner side; in lower teeth 

 (except in the fore-part of 7nj) the converse is the case. In upper 

 teeth certain of the inner salient angles are remarkably and 

 broadly truncated ; and a similar though less conspicuous trunca- 

 tion is shown by certain of the outer salient angles in the lower 

 molars. The upper tooth-row is further remarkable for the 

 great size and especially the great breadth of ?«,^, which is often 

 decidedly larger than m^. The pattern of the upper teeth 

 is as follows : — m^, with three salient angles on each side, 

 consists of an anterior transverse loop and four alternating 

 closed triangles, the first and third being internal and small with 

 truncated tips, the second and fourth being external and normally 

 angular ; 7n^, with three outer and two inner salient angles, 

 consists of an anterior loop and three closed triangles, of which 

 the first and third are external, large, and normally angular, 

 the second internal, small, and squarely truncated; the first 

 outer fold in this tooth is deep and transverse, so that the junc- 

 tion of the first outer triangle with the anterior loop is effected 

 on the inner border of the tooth instead of in the centre of the 

 crown as in normal Microtines, and the first inner salient angle, 

 made up as it is of the inner extremity of the anterior loop and 

 the base of the first outer triangle, has accordingly a remarkable 

 appearance of abrupt truncation ; this last character is reflected 

 in the alveolus, for the alveoli are closely moulded to the teeth, 

 and is often of great practical importance to the palaeontologist 

 when dealing with fragmentary palates from which the teeth 

 have fallen out; m^, with three or four outer and three inner 

 salient angles, consists of an anterior transverse loop followed 

 by four triangles and a small posterior loop ; of the four triangles, 

 the first is external and exactly like that of m^, the first outer 

 infold being transverse so that the junction of this first triangle 

 with the anterior loop takes place on the inner border of the 

 tooth near the centre of the abruptly truncated first inner salient 

 angle ; the second and third triangles are opposed and confluent 

 with each other, and shut off from the first triangle behind by 

 a deep inner fold and a much shallower outer one; the fourth 

 triangle is internal and confluent wath the small posterior loop, 

 which may be regarded as consisting chiefly of a fifth outer 

 triangle; this terminal part of the tooth is separated from the 

 parts in front by a deep inner infold and a shallow or quite 

 vestigial outer fold. In the lower jaw m^, with three outer and 

 four inner salient angles, consists of a posterior transverse loop, 

 three alternating closed triangles (of which the first is internal), 

 and an anterior loop formed of a broadly confluent pair of 

 triangles and a small anterior loop proper ; jh,, with three salient 

 angles on each side, consists of a transverse posterior loop and 

 four alternating closed triangles of which the first and third are 

 internal; w^, with two outer and three inner sahent angles. 



