104 PROF. OWEN ON FOSSIL EVIDENCES 



the Cerithian-nummulitic zone, and consequently older than any 

 other known genus of extinct Sirenians whose bed has been geologi- 

 cally determined. 



The first discovered Sirenian fossils, referred to a Hippopotamus 

 minor and to a Manatus fossilis by Cuvier (the Manatus Guettardi, 

 De Blainville), are from French tertiaries of Miocene age. The 

 Sirenian first generieally separated from living forms, by Kaup, 

 under the name Haliiherium, is from the Miocene of Eppelsheim, 

 near Darmstadt. The Haliiherium Serresii, Gervais {Metaxitherium, 

 De Christol), is a Miocene fossil * ; and Sirenian fossils have been 

 traced in France from the " calcaire grossier" of the Gironde, contain- 

 ing Lophiodont remains, up to the Pliocene near Montpellier. Crassi- 

 iherium robustum, Yan Beneden, is from a formation of Lower Miocene 

 age in Belgium, the equivalent probably of our Hempstead beds f . 



Felsinoiherium Forrestii, Capellini, is from beds at Biosto, in 

 Bologna, regarded by that excellent observer as of Pliocene age %. 



The Sirenian fossils (Rytiodus, Lartet) from the basin of the 

 Garonne, are from Upper Miocene beds §. Prestwich considers the 

 native matrix of the " Halitherium Canhami, Mower," to have been 

 " most likely derived from some Miocene beds which formerly existed, 

 probably in what is now the basin of the German Ocean" ||. 



Dr. Leith Adams has recorded " the discovery of a tooth and ear- 

 bone of a Halitherium in a calcareous bed at Malta "If. The 

 JRhytina Stelleri, Illig. (Manatus borealis, Pall.), " ce trop confiant 

 Sirenien de Pile Behring," lived on the North Pacific Ocean to within 

 the last century. 



We have thus evidence of an almost world-wide distribution of Sire- 

 nian Mammals, under several generic modifications, which has become 

 restricted at the present date to a few tropical or subtropical localities, 

 under the forms signified by the terms Manatus and Halicore. 



In both Lamantins and Dugongs the cerebrum is better developed 

 than it was in Ehytina, and in Rhytina somewhat better than in 

 Eotherium. In the recently extinct Sirenian the excess is at the 

 back part of the cerebrum ** ; in Halicore it is at the fore part. In 

 Manatus both fore and hind parts of the hemispheres are relatively 

 broader and higher than in the extinct Eocene form. 



Viewing fig. 2 in contrast with fig. 5, one is led to speculate 

 on the circumstances influencing increase of brain-mass in marine 

 Mammals of simple, sluggish, Sirenian habits, either obtaining their 

 food from seaweed at no great depth, or shuffling along to browse the 

 grassy shore of a river or estuary. Certain it is that since the good 



* ' Zoologie et Paleontologie Franchises ' (4to, 1849), Descr. des Pis. 4, 5, 6. 



t "Un Sirenien nouveau du terrain rupelien," Bulletin de l'Acad. R. de 

 Belgique, 2 e serie, torn, xxxii. 1871. 



| " Deposito littorale pliocenico di Riosto, litologicamente non solo ma ezian- 

 dio per i fossili e per i rapporti stratigrafici col cretaceo ed il mioceno," Me- 

 morie della R. Accademia delle Scienze dell' Istituto di Bologna, 4to, serie terza, 

 tomo i. p. 609. 



§ " Note sur deux nouveaux Sireniens fossiles des terrains tertiares du bassin 

 de la Garonne," Bulletin de la Soc. Geol. de France, 2 e serie, torn, xxiii. 1866. 



|| Quart. Journ. Geol. Soc. vol. xxx. (1874) p. 7. «|[ Bid. 



** Brandt, op. cit. t. ix. fig. 3. 



