Classification of the Otomjinpe. 207 



may in some cases represent two lamiaal elements ; the 

 total therefore usually four and never more than five. First 

 lower molar composed of four laminae or their equivalents, 

 as in Otomys. 



This genus, although clearly worthy of being distinguished 

 as such, shows more relationship to Otomys than is the case 

 with Parotomys. One species, indeed, M. turneri, both has 

 more expanded nasals than is normal and has clearly five 

 laminae in its m' ; but even theii there is no equality with 

 the specialized condition found in true Otomys, and the 

 frontal ridges are quite as in Parotomys, not as in Otomys. 



The following forms belong to this genus : — 



broomi, Thos. 

 yranti, Thos. 

 slogyetti, Thos. 

 tU7'neri, Wrought. 

 unisulcatus, Bts. 



3. Otomys, F. Cuv. 



Genotype. 0. irroratus, Bts. 



Skull higldy specialized. jNIuzzle with an exaggerated 

 expansion of the nasals in their anterior half, where tliey 

 are bent down laterally, and quite hide the premaxillse from 

 above. Interorbital region contracted, its edges with high 

 ridges, which posteriorly turn abruptly outward to form 

 postorbital processes, and then run backwards across the 

 parietals. 



Teeth. Incisors ranch grooved, the upper with one well- 

 defined groove just outside the middle, the lower with one 

 broad and deep outer groove and on the inner side either 

 the faint indication of a second groove, a shallow but distinct 

 groove, or a deep and distinct second groove, all stages 

 between the three being present. 



Molars Avith great tendency to extra lamination, the 

 third upper molar with from six to ten laminae (five in 

 0. denti only) and the first lower with from four to seven. 



It does not appear possible to separate satisfactorily tlje 

 species with two grooves on the lower incisors (typits and 

 its allies *) from the ordinary Otomys with only one, as the 

 intergradation in the depth and conspicuousness of the 

 grooves is too complete. On the other hand, two species, 

 anchietce and laminatus, show such differences in the number 

 of the molar laminae that I have thought they should be 



* Representing Oreinomys, Trouess. • 



