402 MAMMALIA. 



sea. At present, however, Palaeontology furnishes no definite 

 clue to their origin ; and they are only known to have been 

 already well differentiated in the Pliocene period. A character- 

 istic mandible of a seal from the Upper Pliocene of Moritpellier, 

 France, is named Pristiphoca occitana. Other fragmentary 

 remains are known from Upper and Lower Pliocene strata in 

 different parts of Europe and North America, notably in the 

 Crag of Antwerp (Palceophoca, Callophoca, Platyphoca, and 

 others). A few fragments have been recorded from the Cromer 

 Forest Bed of Norfolk. The walruses also date back to the 

 Pliocene in Europe, an imperfect skull (named Alachtherium 

 cretsi) having been obtained from the Crag of Antwerp, and 

 several characteristic tusks being known both from this forma- 

 tion and from the equivalent Red Crag of Suffolk (Trichechiis 

 huxleyi). A skull of the existing Trichechus rosmarus has 

 been obtained from the fen-land near Ely, a mandible from 

 the Dogger Bank in the North Sea ; and more doubtful remains 

 are known from the Thames alluvium in London. 



ORDER 7. INSECTIVORA. 



The existing small mammals which are adapted to feed 

 upon insects and worms, and are grouped in the order 

 INSECTIVORA, are probably the little-altered survivors of some 

 of the most primitive placentals. They agree with the 

 Creodonta in their low type of brain and nearly always in 

 the separation of the lunar and scaphoid bones of the carpus ; 

 but their canine teeth are comparatively feeble, and when 

 any of the incisors are enlarged these are always the inner 

 pair. Though nearly all the fossils are fragmentary, most of 

 the existing families can be traced back to the Upper Eocene ; 

 but some of the portions of dentition of the extinct genera are 

 very doubtfully determined, and may even be referable to 

 unknown primitive Primates. Neurogymnurus, known by the 

 complete skull, mandible, and dentition from the Upper 

 Eocene Phosphorites of France, seems to have been a hedge- 

 hog of the family Erinaceidae ; while a typical skull of 

 Erinaceus itself is known from the Upper Miocene of Oeningen, 



