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Show 798 MR. F. E. BEDDARD 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 of 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 destruction ; 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. O n the Brain of Hydrochcerus. By F R A N K E. B E D D A R D , M . A V F.R.S., Prosector and Vice-Secretary of the Society. [Received 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 Rodents. Among the more important types which I was unable to study on that occasion was the genus Hydrochcerus. I was able, however, to refer to a published description of this genus accompanied by illustrations by M . Camille Dareste. Inasmuch as Hydrochcerus has the largest aud best convoluted brain of any Rodent2, 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 Hydrochcerus. M. Dareste has represented fairly accurately the external features of the brain, save for one particular: I find that in m y well preserved brains there is no such hiatus as he 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 tbe under surface : one of m y specimens, which was in an exceptionally perfect state of preservation, enables m e to add to Dareste's description and, I believe, improve upon his figure. •n V'^o^ Convolutions of the Cerebral Hemispheres in certain Rodents," P. Z. S. 1892, p. 596. 2 " Note sur le Cerveau des Rongeurs, &c," Ann. Sci. Nat. (4) iii. p. 355. |
