LAGOMORPHA. 877 



gitudinal convexity of the inner aspect of the ramus, which extends along- 

 its inferior border as far as the fourth molar. A shallow groove separate* 

 its posterior half from the inferior border of the ramus. 



The first and last inferior molars are smaller than the others. In the 

 intermediate ones the posterior column is smaller than the anterior one, 

 and is in close contact with it. Both are transverse oval in section, and the 

 anterior is a little more prolonged inwards. The inferior incisor is rounded 

 posteriorly, and narrowed ; in front the surface is very gently convex, and 

 slightly oblique outwards. The enamel is smooth, folds over, forming a 

 band on the outer side, and does not fold over on the inner side. 



The earliest dentition of this species known to me is the presence of 

 the two deciduous molars, the first and second in position, before the appear- 

 ance of any of the permanent series. Each of these has two roots, and the 

 crown is composed of three lobes. In the first, the first lobe is a simple 

 cusp; the two following are divided into two cusps each; the second is sim- 

 ilar, excepting that the simple cusp is at the posterior end of the tooth. The 

 grooves separating the lobes descend into the alveolus on the outer side, but 

 stop above it on the inner. The measurements at this stage are — 



Measurements. 



M. 



Length of two milk-molars , O.OO.'iO' 



Depth of ramus at No. 2 '. 0042 



Depth of ramus at diastema 0032 



In the next stage the third permanent molar is projected, and has, like 

 the second deciduous, a posterior simple column, whose section forms an 

 odd cusp or lobe. The fourth true molar then follows, also with an odd fifth 

 lobe behind. This lobed form of the molars is so ditferent from that of the 

 adult as to have led me to describe it as indicating peculiar species under 

 the name of Tricium avunculus and T. annce. 



In the next stage, the fifth small molar appears in view, and the second 

 permanent molar lifts its milk-predecessor out of the way. In a very short 

 time, the posterior, or odd, columns entirely disappear, sinking into the 

 shaft, and the permanent molars assume the form characteristic of the 

 species. The last stage prior to maturity sees the first milk-molar shed, 

 and the younger portion of the first permanent molar protruded. A speci- 



