Soulh-^ti/icrican Uudents. 4-i3 



often deeply excaviited and ahv.iys readily perceptihle. Tliis 

 slylo of palate is shown in Mr. Ban;^.s'6 figures 1 b and 2 i of 

 the plate quoted. 



In TJiomasomi/s, on the other hand, with whicli I must 

 synonymize Erioryzomys^ Bangs, the mesopterygoid fossa 

 extends further forward (to between the last molars), is, as a 

 rule, rather more squarely open in front than in Oryzomys^ 

 and there are no lateral |»its. Mr. Bangs's figure 3^ shows 

 excellently this type of })alate. 



To the genus as thus defined the following species, 

 mostly described under Oryzomys, prove to be referable, 

 though, of course, the number of mammse is not as yet known 

 in all of them : — 



Tliomasomys prmceps, Thos. 



pneturj Thos. 



aureus, Tomes. 



2\ijrr/io/to(us, Thos. 



vestitus, Thos. 



chif-reuSj Thos. ( Type of genus.) 



■ KaIinoio\sLii, Thos. 



incanus, Thos. 



paramorum, Thos. 



■ Taczanorcskii, Thos. 



• la'ops, Thos. 



niveipesj Thos. 



luniye?', Thos. 



moriochromos. Bangs. (Type of EriuryzomySj 



Bangs.) 



ferrugineuSj Thos. 



dorsalis, Hensel. 



sublineatus, Thos. 



It will be noticed that nearly all tliese species are inhabitants 

 of the mountainous regions of N.W. South America, from 

 Colombia to Peru, none of them penetrating into Central 



latter lateral and paired. To avoid this confusion I would suggest that 

 while the former, the median one, might still be called the mesopterygoid 

 fossa, the new name of parapterygoid might be given to the lateral ones, 

 the names themselves then explaining the positions that the fossae 

 respectively bear to the i-kiiU as a whole. 



Mr. MUler, in figuring a Microtine skull (X. Am. Faun. no. 12, p. 27, 

 1896), has followed the usage of the human anatomists in calling the 

 lateral fossae simply ^'pterygoid," and then using interpterygoid for the 

 median one ; but other authors have used this latter name for the lateral 

 ones, and as the names do not explain themselves, their misuse is always 

 probable. It would therefore seem advisable to drop them altogether 

 and to use terms which are selt-explanatorj'. 



