12 Southern Cross. 



respective teeth. It is evident that, whereas the needs of existence 

 do not tend towards any very great variation in bodily shape, the food 

 of the Fhocidae, or the method of securing- it, may be so varied as to 

 have induced the evolution of many quite distinct types of denti- 

 tion, the production of which postulates great plasticity of the teeth. 

 The result is that the Phocidae have already, by their teeth, shown 

 themselves to be on the road to division into groups corresponding 

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

 rhinus, witii its sinuous body and saw-like teeth, represents the most 

 specialised form of Pinniped Carnivore on a large scale, Ommatoplioca, 

 JErignatus, and Cystopliora feed on more feeble prey, while the 

 smaller Carnivora are represented by Fhoca Idsjpida and P. vitulina — 

 resemblances which seem to suggest all sorts of possibilities in dual 

 evolution, possibilities of the rise of what now appear to be homo- 

 geneous Orders of mammalia independently and in different regions, 

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

 Whalebone and Toothed Whales. 



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



difficult to discover any connection between the grinders of Lohodon 



with their five complicated cusps, and the comparatively simple 



teeth of Fhoca vitulina. We have, however, numerous intermediate 



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



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



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



but small trace of accessory or smaller cusps. Leptonyclwtes is 



relatively the weaker of the two in dentition ; but from very strong 



teeth, of the type of those of P. vitidina, may have been derived the 



(relatively) strongest teeth of the whole group, those of Monachus. 



Diminish the cusps and reduce the size of the teeth, and there 



results the remarkably weak-toothed Ommatoplioca ! Phoca groen- 



landica may be taken as an example of development in another 



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



are not nearly so strongly developed as in Phoca hispida or in 



Ogmorhinus, the triple-cusped teeth of which are examples, the former 



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



of instrument. Finally, there is the complicated arrangement .of 



Lohodon, in which the central cusp is immensely developed at the 



expense of the remainder, and possesses a frequently bulbous and 



recurved apex. The anterior cusp of Ogmorhinus is here represented 



by a small corresponding protuberance, the posterior cusp appears 



as three distinct, rather autero-posteriorly flattened, projections 



runniniT across the width of the tooth. 



