33 



to within less than an inch of the posterior angles of the nasal open- 

 ing. The anterior edge of the post-orbital apophysis and the lower 

 margins of the orbits are plain and smooth, not irregular. The vo- 

 merine sheath is not nearly so prolonged anteriorly, and does not 

 reach to within an inch of the anterior incisive foramen. The max- 

 illary and inter-maxillary do not unite by a bevelled surface, but by 

 a suture forming a right angle. 



On one point we can draw a tabular view of the whole of the 

 skulls, viz. as to the comparative distance of the orbit from the end 

 of the beak, which, compared with the total length of the skulls, is 

 as follows : — 



In Dr. Vogel's entire head of the Ayu as 7 to 36, or about 1 to 5. 

 In the skull from the mouth of the Kwora as 27 to 100, or more 

 than 1 to 4. 



In the skull of M. Senegalensis as 1 to 3 nearly. 



In the skull of M. australis as 5 to 14, or less than 1 to 3. 



From what I have drawn out we may, I believe, make the follow- 

 ing deductions : 1st, That in the Kwora or Niger, and its tributary 

 the Tsadda or Binue, is found a Manatus intermediate in many of 

 its characters between M. aust?'alis and M. Senegalensis ; and 2ndly, 

 That if these differences are, as Prof. Owen suggests, too marked for 

 a mere variety, then there is no alternative but to allow it as a species. 

 I do not mean to affirm its positive existence, but merely following 

 up the idea thrown out by Prof. Owen, in examining the skull I 

 brought home, I think the probability of its distinctiveness is con- 

 siderably increased. Being about to revisit the river Kwora I shall 

 make a point of searching more closely after this animal, with a view 

 to settling the question. If established, the genus will stand as fol- 

 lows : — 



Manatus, Rondel. 



1. Manatus australis, Tiles. 



Hab. West Indies and north-east coast of South America. 



2. Manatus Senegalensis, Desm. 



Hab. African rivers, Senegal to the Gambia. 



3. Manatus Vogelii, Owen. 



Hub. Rivers opening into the Bight of Biafra. 



Whether M. nasutus of Wyman and M. latirostris of Harlan are 

 species, varieties, or synonyms, I have not the means of ascertaining. 



M. australis is, as I have mentioned, more allied to the extinct 

 fossil forms; and M. Senegalensis, again, more approaches in form 

 of skull to the Dugong. 



No. CCCXXIX.— Proceedings of the Zoological Society. 



