224 Bulletin American Museum of Natural History. [Vol. V, 



inner half, gray or grayish white, varying in different specimens, to pure white 

 on the outer half. 



The spines are restricted (in a series of 10 adults) to an oval area on the 

 middle of the back, between the shoulders and the hips, extending laterally on 

 to the sides of the body. The spines are grayish white or whitish at base, 

 passing gradually through gray and dusky gray to black, the exposed portion 

 being black, except on the lateral portions of the spiny area, where the spines 

 are often whitish nearly to the tip. 



Measurements (average of five specimens measured in the flesh). Total 

 length, 446 mm. ; head and body, 244 ; tail, 202 ; hind foot, 50 ; ear from 

 crown, 23. The males average somewhat larger than the females, as shown by 

 the subjoined table. 



Young. One-third grown young (in the 2-molar stage) are blackish above, 

 nearly pure black over the central portion of the dorsal area, paler, brownish 

 black on the sides, where the dusky tint has a purplish or faint vinaceous 

 tinge ; below white, with or without a dusky prepectoral collar, traces of which 

 are sometimes present in the adult. The whole pelage is spineless' and soft. 

 When about half-grown (in the 3-molar stage) the sides become faintly tinged 

 with pale rusty brown, and a few weak spines begin to appear in the middle of 

 the back. At a more advanced stage the general coloration above is still dusky 

 brown, with a blackish spiny area over the middle of the back (between the 

 hips and shoulders), with rusty-tipped hairs more or less generally intermixed 

 over the whole upper surface of the body. 



Skull. An average adult skull measures as follows : basal length, 48 mm. ; 

 greatest breadth, 29 ; least interorbital breadth, 13.3 ; length of nasals, 24 ; 

 diastema (distance between incisors and first molar), 14 ; upper molar series, 10. 

 The nasal bones extend considerably beyond the fronto-maxillary suture, and 

 are squarely truncate or slightly rounded on the posterior border. A series of 

 young skulls shows the development of the molar series from two to four teeth. 



?ype, No. fljf, $ ad., Princestown, Trinidad, April 26, 1893, coll. Frank 

 M. Chapman. 



This species is based on a series of 21 specimens 12 adults, 

 five young in the spineless, soft, hairy coat, and four in inter- 

 mediate stages between the spineless young and the fully adult. 

 Two of these are preserved in alcohol, the rest as skins with the skulls 

 separate. All were taken at Princestown during March and April. 



Echimys trinitatis differs from . cayennensis, its nearest geo- 

 graphical congener, in various external characters, notably in the 

 restriction of the spiny area to the central portion of the back, 

 in the less hairy condition of the tail and the entire absence of a 

 hairy pencil at the tip, and also somewhat in coloration, especially 

 in the absence of a pale rufous patch behind the ears. In cranial 



