798 ME. F. E. BBDDABD ON THE [June 20, 



point I do not wish at present to express a definite opinion), the 

 probability is that it was at least an extinct species, if not a genus. 

 Could the existence o£ a St. Helena Sirenian be definitely 

 determined, it would be of much interest in regard to the history 

 and distribution of the group. Mr. Sterndale, who is convinced 

 that the creature was a " Manati," has promised to make a thorough 

 search in the island for any remains that may have escaped de- 

 struction ; but I fear that any successful results are in the highest 

 degree improbable. The best chance would be to thoroughly 

 examine the shore at Manati Bay, especially if there are any raised 

 beaches. 



8. On the Brain of Hyd^'ochcerus. By Frank E. BeddarDj 

 M.A., F.R.S., Prosector and Vice-Secretary of the 

 Society. 



[Eeceived June 6, 1899.] 



In a communication made to this Society some years since ^ 

 I dealt with the cerebral convolutions of a considerable number of 

 genera of Eodents. Among the more important types which I 

 was unable to study on that occasion was the genus Hydroclioerus. 

 I was able, however, to refer to a published desci'iption of this 

 genus accompanied by illustrations by M. Camille Dareste. Inas- 

 much as Hydroclioerus has the largest and best convoluted brain of 

 any Rodent ^, and as I have been able to study three excellently 

 preserved brains extracted from specimens which have died in the 

 Gardens, I think it worth while to add what I find myself in a 

 position to do to Dareste's relation and interpretation of fact. 



That author had two brains at his disposal, but has only figured 

 the dorsal aspect of one. His paper also contains figures of a 

 lateral and a ventral view. 



General External Features of the Brain of Hydrochoerus. 



M. Dareste has represented fairly accurately the external features 

 of the brain, save for one particular : I find that in my well pre- 

 served brains there is no such hiatus as lie figures between the 

 cerebral hemispheres and the cerebellum. The somewhat pointed 

 anterior end of the cerebellum fits in fairly closely between the 

 divergent extremities of the cerebral hemispheres. Moreover the 

 general outline of the hemispheres is by no means so triangular as 

 he has represented it to be. It is indeed almost a hexagon, of a 

 much more graceful figure. 



As to the under surface : one of my specimens, which was in an 

 exceptionally perfect state of preservation, enables me to add to 

 Dareste's description and, I believe, improve upon his figure. 



1 " On the Convolutions of the Cerebral Hemispheres in certain Eodents," 

 P. Z. S. 1892, p. 596. 



2 " Note sur le Cerveau des Rongeurs, &c.," Ann. Sci. Nat. (4) lii. p. 355. 



