0E AN EOCENE SIEENIAN MAMMAL. 105 



old Eocene times " new foes have arisen ; " and any increase in the 

 number of creatures and their lethal powers concerned in killing 

 sea-cows would add to the number of phenomena which such sea- 

 cows were concerned in noting, with concomitant reaction of such 

 perceptions, or neural vibrations, resulting in a change of cerebral 

 into muscular force, exercised to put themselves into depths of 

 safety. With such augmentation of ideas, i. e. of sensations and 

 volitions, in surviving modern Sirenians, the thinking organ has 

 grown ; and this hypothesis or explanation may apply to analogous 

 instances in other time-series of herbivorous Mammals. 



EXPLANATION OF PLATE III. 



Fig. 1. Side view of a caBt of brain of Eotherium cegyptiacum. 



2. Upper view of ditto. 



3. Under view of ditto. 



4. Section of myelon. 



5. Upper view of a cast of brain of Manatus americanus. 



6. Under view of cerebrum. 



{All the figures are of the natural size.) 



Discussion. 



Dr. Mtjeie explained the distinctive characters of the four genera 

 of Sirenian Mammals, Manatus, Rhytina, Halicore, and Halitherium, 

 and stated that he regarded Halitherium as the highest form, seeing 

 that it was a four-limbed type. He remarked that in the young 

 Manatus the brain differs in form from that of the adult, which was 

 a fact to be considered with reference to the data on which Prof. 

 Owen's deductions were founded. 



Mr. Seeley said that he had no doubt the brain was Sirenian, and 

 indicative of a new genus. The existing genera differed from it, in 

 his opinion, in having the Sirenian characters more strongly marked 

 rather than in showing a higher cerebral type. In general form 

 the brain reminded him rather of a Carnivore than of a Sirenian ; 

 and he thought it indicated affinity with a generalized Carnivorous 

 type more than with the living Sirenians. 



Mr. Baueeman stated that the section from which this fossil was 

 obtained is about 600 feet high, but the quarries referred to by the 

 author were within about 100 feet of the top, in what had been 

 regarded by Dr. Le Neve Foster and himself as a shallow- water 

 deposit. The lower parts of the Cliff are very like the Chalk with 

 flints, except that they contain Nummulites. 



Mr. Chaeleswoeth remarked that the fossil now before the Society 

 was exceedingly interesting, as indicating the extension backwards 

 in time of the Sirenian type. He stated that he did not believe that 

 the English Halitherium Canhami was of Miocene age. 



Dr. Leith Adams said that the Maltese Halitherium was truly 

 Miocene. 



Prof. Owen briefly replied, and concluded by hoping that the 

 objections to any of his conclusions, if reported, would be accom- 

 panied by their grounds. 



