20 



MR. R. LYDEKKER ON A JAW OP HTOTHERIUM. 



species of that genus, since its distinctness from the American 

 forms may be taken for granted. Before, however, making this 

 comparison, it is necessary to observe that I have already described 

 and figured* a fragment of the mandible of a Hyotherium from 

 Perim Island f containing the second true molar, which, from the 

 great relative width of the tooth, I considered might probably 

 indicate a new species. Since the tooth of that specimen agrees 

 precisely in relative size with the corresponding molar of the jaw 

 under consideration, it may be safely regarded as belonging to the 

 same species. 



With regard to the European species the present form is distin- 

 guished from H. typum % (rauging from the Quercy phosphorites to 

 the Middle Miocene of Georgensmiind) not only by its superior size 

 but by the production of the postero-internal angle of the third 

 upper true molar. Confining these comparisons to the larger species 

 like H. WaterJtousei and H. Soemmering!, it will be found that the 

 present form agrees with the first-named species § in size, but is 

 distinguished by the relatively wider teeth, the presence of four 

 distinct columns on m. 3, the greater development of the accessory 

 columns, and the absence of an inner cingulum to the upper true 

 molars. With regard to H. Soemmering! || the upper molars of our 

 specimen are rather smaller than the teeth of that species figured 

 by Peters in the ' Denkschr. k. Ak. Wiss. Wien,' vol. xxix. pi. i. fig. 1, 

 but are otherwise very similar, m._3 of the Perim jaw agreeing 

 very closely with the specimen represented in fig. 3 of the same 

 plate. The upper teeth appear, however, rather wider than those 

 of H. Soemmering!, and the lower molar is decidedly wider. This 

 difference, coupled with the improbability of a species which died 

 out in Europe after the Middle Miocene being identical with an 

 Indian Pliocene form, renders it probable that the present form 

 is distinct from H. Soemmering!, although it is certainly allied. 



The only species from India to which a distinct name has been 

 assigned is H. sindiense which occurs in the Lower Siwaliks of 

 Sind. The typical specimens of that species indicate an animal 

 equal in size to the largest race of H. Soemmering!, and apparently 

 so closely allied that it is very difficult to find any distinctive 

 characters from the cheek-teeth on which the species is founded. 

 With these typical specimens are found other teeth in regard to 

 which it is uncertain whether they belong to smalL individuals of 

 the same or to a distinct species ; the associated lower teeth (which 

 may belong to both the larger and smaller forms) are of a much 

 narrower type than the lower molar from Perim. The type 



* ' Palseontologia Indica ' (Mein. Greol. Surv. Ind.), ser. 10, vol. hi. p. 97, 

 pi. xii. fig. 5. 



t The specimen was reported to be from Perim Island, and its mineral con- 

 dition indicates that this is certainly correct. 

 \ Syn. H. Meissneri.t 



§ See Filhol. ' Ann. Sci. Greol.' vol. xi. art. 1, pi. vi. (1880). 

 !| Syn. PalcBOchcerus major, Pomel. 



■[[ ' Palasontologia Indica,' op. cit. pp. 95-97, pi. xii. . ' 



