COPE.] PALEONTOLOGY ^MIOCENE PERIOD. 479 



There is the merest trace of a posterior lobe at this time, and that speed- 

 ily disappears. The anterior lobe is subconical, and is entirely sur- 

 rounded with enamel. By attrition, the two lobes are speedily joined by 

 an isthmus, and for a time the tooth presents an 8-shaped section, which 

 was supposed to be characteristic of the 'genus. Further protrusion 

 brings to the surface the bottom of the groove of the inner side of the 

 shaft, so that its section remains in adult age something like a B. 

 Ths measurements of a medium-sized adult are — 



Measurements. 



M. 



Length of inferior molar series 0.012 



Length from M. 1 to end of incisor 012 



Length of diastema 008 



Length of crown of M. 1 0029 



Elevation of crown of M. 1 above alveolus 0035 



Depth at M. 1 ' .0070 



Depth at M. 5 0085 



Liferior diameter of ramus helow M, 1 0040 



Several hundreds of specimens of this species were observed. 



Pal^olag-us tuegidus, Cope, Pal. Bull., IsTo. 16, p. 4. Tricium pa- 

 niense, Cope, loc. cit., p. 5. 



The largest species of the genus. Molars with two simple columns, 

 the first and fifth grooved on the outer side only 5 the interior grooves 

 of the others weaker. A porous enlargement on the inner inferior part 

 of the ramus just behind the symphysis. Diastema obtuse. 



Measurements. 



M. 



Length of molars 0.016 



Length of three median molars 010 



Depth of ramus at central molars Oil 



Width of central tooth 0035 



The deciduous molars present much the same character as in P. hay- 

 denii, except that there is scarcely a trace of the odd posterior tubercle 

 on the second. The posterior root of the latter extends to the bottom 

 of the alveolus. The grooves of crown do not descend to the alveolus 

 on either side. Measurements of such a specimen are — 



Measurements. 



M. 



Length of two anterior molars 0.0068 



Length of first molar 00.32 



Width of first molar 0021 



Depth of ramus at first molar 0085 



Depth of ramus at diastema 0061 



Pal^olagus triplex, Cope, Paleontological Bulletin, l^o. IG, p. 4. 



This species rests on characters which I have observed to be tran- 

 sitional in the P. haydenii, and I have attended to the possibility of the 

 individual which has furnished them being- a similarly immature P. tur- 

 gidus. In a considerable number of specimens of the latter, no approach 

 to the present one is exhibited ; the latter is a fully-grown animal, and 

 its characters would remain after considerable attrition of the teeth has 

 been reached ; size of the last 5 first and last molars deeply grooved 

 on both sides, as well as all the rest 5 first molar with a trifolium-lobate 



