Zoological Society. 451 



dification of the female generative organs in a specimen of the Ma- 

 cropus Bennettii dissected by him at the University of Gand *. 



The brain of the Dendrolagus inustus weighed 6 drachms. 



The cerebral lobes were smooth, and showed only a short linear 

 indentation above the anterior part of each. There was no trace of 

 supra-ventricular commissure (corpus callosum), and in all particu- 

 lars save the more simple external surface the structure of the brain 

 corresponded with that of the Great Kangaroo as described in the 

 'Philosophical Transactions' for 1837. The proportion of the 

 weight of the brain to that of the body is as 1 to 230 ; in the Ma- 

 cropus major it is as 1 to 800, the comparison being made on the 

 body of a large old male. The difference between the large and 

 small species of Kangaroo depends on the brain not increasing in 

 proportion to the increase in the bulk of the entire animal. The 

 smaller species in any natural family of Mammalia, resemble the 

 foetus of the larger species in the greater proportional size of both 

 the brain and the eyes. 



On the Monkeys of the Amazon. 

 By Alfred R. Wallace. 



The great valley of the Amazon is rich in species of Monkevs, and 

 during my residence there I had many opportunities of becoming 

 acquainted with their habits and distribution. The few observations 

 I have to make will apply principally to the latter particular. I have 

 myself seen twenty- one species ; seven with prehensile and fourteen 

 with non-prehensile tails, as shown in the following list : — 



3 Howlers, viz. — Mycetes ursinus, M. car ay a 1 and M. Beelzebub ; 

 1 Spider Monkey, — Ateles paniscus ; 



1 Big-bellied Monkey (Barrigudo of the Brazilians), — Lagothrix Hum- 



boldtii ; 



2 Sapajou, — Cebus gracilis (Spix) and C. apella 1 ; 



4 Short-tailed Monkeys, — Brachyurus couxiu, B. ouakari (Spix), 



B. rubicundus (? Calvus, B. M.), and a new species ; 



2 Sloth Monkeys, — Pithecia irrorata and an undescribed species; 



3 Squirrel Monkeys, — Callithrix sciureus, C. personatus and C. tor- 



quatus ; 



2 Nocturnal Monkeys, — Nyctipithecus trivirgatus and N. fel 'in us ; 



and 



3 Marmoset Monkeys, — Jacchus bicolor, J. tamarin and a new spe- 



cies. 



The Howling Monkeys are generally abundant ; the different spe- 

 cies, however, are found in separate localities ; Mycetes Beelzebub 

 being apparently confined to the Lower Amazon, in the vicinity of 

 Para ; a black species, M. carayal, to the Upper Amazon ; and a red 

 species, M. ursinus, to the Rio Negro and Upper Amazon. Much 

 confusion seems to exist with regard to the species of Howlers, owing 

 to the difference of colour in the sexes of some species. The red and 



* Bulletin de l'Academie Royale de Belgique, torn, xviii. p. 599. 



29* 



