CM 



m a 



iparate locality and, most 



period, 



justice of these conclusions becomes 

 discussed in detail 



this div 



55 



probably 



und 



unlik 



d 



more apparent when the remainin 



and then analysing the latter 



i. The 



M . . ~. sections are 



More is gained therefore by merely comparing the distribution of 



am 9 



with that of the remaining sections 



ijointly, as shown in d 



■v * 



y 



DIAGRAM 8. 





DIAGRAM 9. 



Distribution o( the Bidrntatjb and 



A VODOViJB conjointly. 





Total ... 

 Percentage 



• •• 



... 118 up 



♦67 



Caucasus 

 33-3%. 



The Bidenta™ and the Anodontjs are 



posed entirely of beakless form 



and 



therefore diagram 9 practically 



peats the lower percentag 



already exhibited in 



diagram 3 



Th 



differences 



dne to localisation, 



to their other natural affinities 



of 



beakless form in the section 



Siphonanthje and of thirteen more in the section 



Rhyncholopile 



The most 



otable features of the diagram are 



(1) the high percentage in 



the Circumpolar province 



(2) the gradual decrease along 



the meridians of distribution save one; and 



the 



gradual increase 



along that one (th 



Siberio-Caucasus) meridian 



Th 



evidence 



dy 



dduced from morphology, that the beakl 



type of 



is the more archaic one, is 



,borated by the 



region, 



where the forms still experience 



n 



atural 



the circumpolar 

 ditions such as probably prevailed 



high percentage in 



\ 



i 



