FOSSIL LEPOPJD^5-PALiEOLAGDS. 375 



posterior simple column, whose section forms an odd cusp or lobe behind. 



The fourth true molar then follows, also with an odd filth lobe behind. This 



lobed form of the molars is so different from that of the adult as to have led 



me to describe it as indicating peculiar species under the name of Tritium 



avunculus and T. anna. 



"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. There is the merest trace of 



a posterior lobe at this time, and that speedily disappears. The anterior lobe 



is subcorneal, and is entirely surrounded 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." 



PAL^EOLAGUS AGAPETILLUS Cope. 



ralmolagus agapelillus Cope, Palaeont. Bull., No. 15, 1873, 1 ; Ann. Rep. U. S. Geol. Surv. Terr, for 1873 

 (1874), 478. 



Smaller than P. haydeni, but more robust, with larger incisor teeth. Molars 



all composed of two columns. Founded on a mandibular ramus, with the 



first and last permanent molars just protruding. From the Miocene deposits 



of Colorado. 



PALyEOLAGUS TURGIDUS Cope. 



Palceolagw turgidus Cope, Palaeont. Bull., No. 16, 1873, 4 ; Aud. Rep. U. S. Geol. Surv. Terr, for 1873 



(1874), 479. 

 Tritium paniense Cope, Palaeont. Bull., No. 16, 1873, 5. 



Larger than P. haydeni, but otherwise not much different. From the 

 Miocene deposits of Colorado. 



PAL^EOLAGUS TRIPLEX Cope. 



Palawlagus triplex Cope, Palaeont Bull., No. 16, 1873, 4 ; Ann. Rep. U. S. Geol. Surv. Terr, for 1873 



(1874), 470. 



Similar in size to P. haydeni, from which, however, Professor Cope 

 regards it as distinct. From the same Miocene deposits of Colorado. Known 

 only from an imperfect mandibular ramus. 



