158 MR. ST. GEORGE MIVART ON MICRORHYNCHUS. [Mar. 13, 



inferior molars. It has four main cusps, the anterior of the two in- 

 ternal ones being opposite the interspace between the two external 

 ones. A transverse ridge connects the postero-internal cusp with the 

 postero-external one, and another connects the antero-external with 

 the antero-intemal one, in addition to which an oblique ridge con- 

 nects the postero-external with the antero-internal cusp. The antero- 

 external cusp is divided into two processes, the internal one of which 

 is almost on a line with the two internal cusps, so that the tooth may 

 be said to have two external and three internal cusps. The cingu- 

 lum is very rudimentary within and little marked without. The an- 

 terior main cusps are subequal in height ; but the postero-internal is 

 higher than the postero-external cusp. The posterior part of the 

 tooth is considerably broader than the anterior. 



The homologous tooth in Indris is quite similarly formed. 



Fig. 5. 



Left half of mandible. Scale, nat. size. 



The second lower molar is like the preceding, except that the 

 transverse diameter of the anterior part equals that of the posterior 

 part, that the antero-internal cusp is considerably more extended 

 vertically, and that the supplementary anterior cusp is very much 

 smaller or absent*. 



The same tooth of Indris is similar, except that the supplementary 

 cusp and oblique ridge are both absent. 



The last lower molar is like the second one ; only the supplemen- 

 tary lobe is entirely obsolete, and there is a minute third posterior 

 lobe at the middle of the posterior margin, making the tooth quinque- 

 cuspid. There seems also to be no oblique ridge. In Indris the 

 last lower molar is similar, except that the fifth cusp is more deve- 

 loped. 



inch. 



Length of the anterior upper incisor *08 



Breadth „ „ '03 



Length of the posterior upper incisor "10 



Breadth „ „ "05 



Interspace between the two median incisors • 1 7 



Antero-posterior diameter of upper canine at its base *12 



Extreme antero-posterior diameter of upper canine "15 



Vertical extent of upper canine *15 



Extreme width from within outwards "08 



Antero-posterior diameter of anterior upper premolar at its base *16 



* It is smaller on one side, and absent on the other side of the specimen de- 

 scribed. 



