12 



SoutJic^n Cross. 



n-fl|H?olivu toclh. It is evident tliiit, whereas the needs of existence 

 ,ln not iciul U.wanlsiiny very ^Teat variation in bodily shape, the food 

 i.f the VhiKidat, or the method of securing it, may be so varied as to 

 have indnced the evolution of numy quite distinct types of denti- 

 tion, tlie priHluction of which j.ostulates great plasticity of the teeth. 

 Th.' n-sult i3 that the Phoddac have already, by their teeth, shown 

 Ives U) he on the road to division into groups correspondiug 

 with some of those of the terrestrial mammalia. Thus, while Ogmo- 

 rhtnm. with its sinuous body and saw-like teeth, represents the most 

 8|RH.-ialiscd form of Pinniped Carnivore on a large scale, Ommatoplwca, 

 Kr . and Vystophora feed on more feeble prey, while the 



.siii.iii. I i.arnivora are represented by I'hoca hispida and P. vitulina— 

 n-seniblances which seem to suggest all sorts of possibilities in dual 

 c\..lution, pos.sibilities of the rise of what now appear to be homo- 

 geneous ( )rders of mammalia independently and in different regions, 

 just as Dr. Kiikenthal believes may have been the case with the 

 Wlialehone and Toothed Whales. 



As regards the modifications of the teeth, it is, at first sight, 

 ilifficult to discover any connection between the grinders of Lohodon 

 with their five complicated cusps, and the comparatively simple 

 I. ..?|, .,f phuca vitulina. We have, however, numerous intermediate 

 ^ whence we may gain some insight into the relationship of these 

 two, and of other forms. Thus, in Lejytonychotes and Phoca vitulina 

 the teeth are simple, the central cusp is all prominent, and there is 

 but small tr.ice of accessory or smaller cusps. Leptonycliotes is 

 n-latively tlie weaker of the two in dentition ; but from very strong 

 teeth, of the tyi>e of those of P. vitulina, may have been derived the 

 (n-latively) stmngest teeth of the whole group, those of Monachus. 

 l)iniinish the cusps and reduce the size of the teeth, and there 

 rt'i^ults the reniarkalily weak-toothed Omiiiatophoca ! Phoca groen- 

 laiulira may be taken as an example of development in another 

 direction, fur here there are distinct accessory cusps, although they 

 ore not nearly so strongly developed as in Phoca hiapida or in 

 f^lfmorhiiiu.s, the triple-<.-usped teeth of which are examples, the former 

 on a small, the latter on a large scale, of precisely the same type 

 tif Miient. Finally, there is the complicated arrangement of 



'- i«» wliieh the central cusj) is immensely developed at the 



'■ "f the remainder, and i»osse.sses a fre(iuently bulbous and 



vwl a|»ex. The anterior cusp of OymorhiiuLs is here represented 

 small cnrresiH)nding protuberance, the posterior cusp appears 

 distinct, rather autero-posteriorly flattened, projections 

 uTosis the width of the tooth. 



