Mammals from British Guiana. 153 
dark collar of the same grey as the sides. Eyes with 
indistinct whitish rings. Ears thinly haired, whitish. 
Limbs grizzled grey like body, lightening to nearly white on 
the fingers and toes. 
Skull and teeth not definably different from those of the 
true C. porcellus. 
Dimensions of the type :— 
Head and body 275 millim.; hind foot, s. u. 43, c. u. 46; 
ear 19. 
Skull: greatest length 59; basilar length 49; greatest 
breadth 35:5; nasals 22x 9; palate 28; diastema 17; length 
of molar series (alveoli) 14°5. 
Type. Male. B.M.no.1.6. 4.120. Killed 7th December, 
1900. 
The difference in colour between this Guianan cavy and 
the Brazilian one is very considerable, but there is a striking 
agreement in other characters. 
25. Myrmecophaga jubata, L. 
Mount Roraima, 5000 feet. 
26. Didelphis marsupialis, L. 
Three skins. 
There appears to be no difference between these specimens 
and skins from the coast-region of Demerara. 
In spite of the arguments brought forward by Dr. Allen in 
his most recent publication on the subject, I still think that 
the Guianan opossum should be regarded as the type form 
of Linneus’s D. marsupialis. 
The evidence of the sixth edition of the ‘ Systema,’ where 
Seba, and Seba only, is quoted, shows what animal Linneus 
had in his mind when speaking of D. marsupialis. The 
interesting fact, to which Dr. Gill has drawn my attention, 
that Linneeus worked under Seba in arranging the latter’s 
collection, adds weight to what we find in his works as to the 
importance of the Seba collection in the preparation of his. 
arrangement of the species of Didelphis. 
27. Metachirus opossum, L. 
One skin from the Rupununi River, 27th September, 
200 feet, and four from the Kanuku Mountains, 300 and 600 
feet, November and December. 
28. Metachirus nudicaudatus, Geoff. 
Two skins, unfortunately both quite young. 6th De- 
cember. 600 feet. 
