270 Mr. O. Thomas on soyne of the 



to be tlie same smaller form, althougli a third skin received 

 shortly afterwards, and also referred to S. quachil^ now appears 

 to be a young individual of the larger. 



Of this larger form the Museum possesses some excellent 

 skins from Guatemala, collected by Mr. Salvin in 1865 and 

 1873, being tliose mentioned by Mr. Alston*, and 1 propose 

 to take the best of them as the type. 



Geomys grandis^ sp. n. 



Size very large, exceeding that of any other known species. 

 Fur coarse, as in G. hisjyidus. Colour smoky chocolate- 

 brown throughout, except on the muzzle, cheeks, and chin, 

 where the hairs are white or pale whitish brown. Inter- 

 mixed with the brown dorsal hairs there are, however, a 

 certain number of pure white ones, and these seem to be most 

 numerous in summer specimens. No darker patches round 

 ears. Hands and feet very thinly haired, the few scattered 

 bristles whitish. Tail absolutely naked. 



Skull large and heavily built (see measurements). As- 

 cending processes of premaxillaries surpassing the nasals by 

 about a quarter of an inch ; the space between them behind 

 the nasals less than the breadth of one of them. Interorbital 

 space broad, as broad as the muzzle, its edges anteriorly 

 rounded and intlated in a manner quite unique f. Zygomata 

 not very widely expanded in proportion to the size of the 

 skull. 



Incisors pale yellow or whitish, in marked contrast to the 

 deep orange found in the allied species. Their single groove 

 deep and very widely open, so that its greatest width on the 

 cutting-edge amounts to 2 millim. ; in position the bottom of 

 the groove is internal, the breadth of the inner portion of the 

 tooth being about 43 to 45 per cent, of the whole % ; owing, 

 however, to the great breadth of the groove itself, it conside- 

 rably overlaps the median line_, but the above percentage is 



* Biol. Centr.-Amer., Mamm. p. 160. 



t Most iiufortunatel}' the " blow of a machete or bush-knife," with 

 which the Indians killed the specimens brought by Mr. Salvin, has exactly 

 destroyed the interorbital region in all the specimens except the type; I 

 am therefore unable to vouch for the constancy with which the peculiar 

 supraorbital inHatiou is present. 



J The position of the incisor grooves both in this and other genera 

 may be accurate!}' defined by measuring the distance from the bottom of 

 the groove to the outer edges of the tooth, and then, the whule breadth 

 of the tooth being taken as 100, the proportional breadths of the inner 

 and outer portions may be readily calculated. The inner portion per- 

 centage of G. mexicaniis rises to 47-50, while in G. hispidus it sinks to 

 about 33. 



