MAMMALIA. 17 



in North America, by peculiar lowly Carnivora with a Table-case 

 comparatively small brain, in which the cerebral liemi- ^^* 

 spheres are nearly smooth and do not cover the mid- 

 brain. In these animals there is no special " sectorial " 

 or " carnassial " (flesh-cutting tooth) near the back of the 

 jaw, and the whole dentition is very similar to that of 

 the flesh-eating pouched animals (Marsupialia) now living 

 in Australia and Tasmania. They were, in fact, regarded 

 as Marsupialia for many years, until it was discovered 

 that some of them possessed a complete milk-dentition 

 which was replaced by the usual permanent teeth. The 

 existing Marsupialia never have more than one milk-tooth 

 replaced on each side of either jaw. 



These Creodonta (" flesh-teeth "), as they are termed, were 

 sometimes as large as lions or bears, and survived in the 

 nortliern hemisphere at least until the beginning of the 

 Miocene period. A typical series of remains, chiefly of the 

 Upper Eocene and Oligocene genera Hysenodon (Fig. cS) and 

 Pterodon, is shown in Table-case 2a. A fine jaw of a large 

 Pterodon from the Upper Eocene of Egypt is especially 

 noteworthy. 



The so-called Sparassodonta from the early Tertiary 

 of South America seem to have been (Jreodonts in which 

 only one or two of the premolars and the canine were 

 preceded by milk-teeth. A skull and portions of jaws of 

 P>orluj8en(i and Prothylacinus, from the Santa Cruz Formation 

 of Patagonia, are exhibited in Table-case 2a. 



Sub-order 3. — Pinnipedia. 



The seals, walruses, and their allies are scarcely repre- Table-eases 

 sented among fossils, and no important ancestors are known. 1^' ^• 

 The tusks of a large walrus (Trichecodon huxleyi) have been 

 found in the Pliocene Ked Crag of Suffolk (see Table-case 

 1a). a few fragments of seals from the Norfolk Forest 

 Bed are sliown in Talile-case 3 ; and with tliese are plaster 

 casts of other remains from the Pliocene Crag of Belgium. 



Order TII.-INSECTIVORA. 



Among the fragmentary fossil remains of the shrews. Table-case 

 moles, and hedgehogs, there are none of much interest ; but ^' 



they date l)ack at least to the close of the Eocene period. 



C 



