PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



front of the incisive foramen is either wanting, or else has a more posterior 

 position than in P. divisus. The palate is less concave transversely and the 

 median ridge is less prominent than in the latter, while the posterior nares 

 do not extend so far forward. 



MEASUREMENTS. 

 Upper dentition, length pA-m& ....... 015 Palate, width at m& ................. 009 



Upper incisor, width ................ 0025 Rostrum, width at base ............. 013 



" " thickness ............. 0x335 " " '.' anterior end ...... .010 



Palate, width at p ................. 004 " dorso-ventral height ........ 009 



PROLAGOSTOMUS IMPERIALIS Ameghino. 



(Plate LXVIII, Fig. 19.) 



Prolagostomus imperialis Amegh.; Enumeracion sistem., etc.; 1887, p. 12. 

 This species is known only from mandibles, the best preserved of which 

 is No. 9,587 of the American Museum's collection. It is distinguished 

 not only by being the largest known species of the genus, but also by 

 the slenderness of the incisors, which are actually thinner than in P. pro- 

 fliiens and are therefore relatively much smaller. Another distinction 

 from all the preceding species is the relative size of the grinding teeth, 

 the series of which is proportionately longer, making up more than half 

 of the total distance from the incisor to the last molar, while the sym- 

 physial region is relatively shorter. The premolar is small ; m 5 has a 

 much greater antero-posterior length than any of the others, but it is 

 somewhat narrower than 



MEASUREMENTS. 

 Lower dentition, length .............. 036 Lower incisor, thickness .............. 003 



" " " Pj-mj ........ 019 Mandible, depth at p T ............... oil 



Lower incisor, width ................ 0025 " thickness at p^ ............. 007 



PROLAGOSTOMUS OBLIQUIDENS sp. nov. 



The type of this species is unfortunately a mere fragment of the man- 

 FlG 2 dible, containing the incisor and the premolar, 



but the latter is so peculiar and characterisistic 

 that the distinctness of the species is open to little 

 Type of Prolagostomus doubt. In size, the present species is about the 

 obliquidens; mandible, crown same as p i m p e n a lis, but the premolar is much 



narrower and is so rotated that its long diam- 

 eter is almost coincident with the axis of the jaw, a character which is 



