1 90 1.] Allen, New Opossums of the Genus Metachirus. 217 



As shown in the tables of measurements, there is considerable 

 variation in size, and some in proportions, in animals that have 

 reached maturity, measurements being given of no specimens in 

 which the last molar has not come into use, with other evidences 

 of maturity. The largest specimen, which has perhaps unfortu- 

 nately been taken for the type, is equalled in size by a single 

 specimen from Greytown, also an old male. The ratio of length 

 of tail to length of head and body varies in specimens from the 

 same locality, as at Metlaltoyuca, Puebla, from 94 to 115, with a 

 total range of variation in this respect from 94 to 119, the aver- 

 age being 109. In young and middle-aged skulls there is barely 

 a trace of a sagittal crest, but in old males it attains a height of 

 2 to 3 mm. The postorbial processes are but slightly developed 

 in early life, reaching only a moderate development even in old 

 age. The postorbital constriction is much less than in the 

 allied genus Didelphis, to which in many respects the skull is 

 closely similar. The nasals, however, are more pointed, both 

 posteriorly and anteriorly, terminating at both extremities in at- 

 tenuated points. The large series from Teapa and Frontera, 

 Tabasco, appear not to show any average difference, either in 

 coloration or size, from specimens from Metlaltoyuca, Puebla, 

 and further subdivision of the material seems at present un- 

 necessary. 



Metachirus grisescens, sp. nov. 



Type, No. 15072, Am. Mus. Nat. Hist., 9 adult, Rio Cauca, Colombia, 

 June, 1899 ; J. H. Batty. 



Somewhat similar to Metachirus fuscogriseus pallidus, but much paler 

 throughout with the tail uniform dark brown, not light at the tip as in the M. 

 fuscogriseus group. General coloration above gray, varied with black ; below 

 whitish, with a slight buffy suffusion ; eye spots and head markings as in M. 

 fuscogriseus, the black, however, less intense, and much less extended pos- 

 teriorly. While the general coloration above is blackish varied with gray in 

 M. fuscogriseus, in the present species it is gray varied with blackish. 



Measurements (from the dried skin). Total length, 510 ; head and body, 

 260 ; tail, 240 ; tarsus, 38 ; tail ratio, about 91. These measurements are only 

 approximate, as the tail is not wholly filled out and the specimen is not well 

 prepared, the skin evidently being much shrunken. The ears are small, about 

 20 by 17 mm. in the dry skin. 



Skull. The skull differs from that of Metachirus fuscogriseus in the great 

 expansion of the posterior portion of the nasals, which maintain a uniform 



