KR. BONNEVIE 



[REP. OF THE "MICHAEL SARS" NORTH 



Fig. 11. Curves showing the variation of "slenderness" in Limacina balea - and in Limacina retroversa . 



The abscissae give the value of the columella projection, the greatest breadth of the shell being represented by the number 10, 

 while the ordinates give the number of individuals within each group of shells. 



A: 100 individuals of each form taken at random. 

 B: 60 full-grown individuals of each form. 

 C: Combination of A. and B. 160 individuals. 



the above review of the literature it is just the degree of 

 slenderness, i. e. the size of the last whorl compared with 

 the rest of the shell, that has been considered the main 

 characteristic of each species. 



In order to prove the range and value of these 

 variations, I have measured, as accurately as the minuteness 

 of the objects admit, the dimensions of 160 specimens 

 of each form. The shells were placed with their mouths 

 upwards (textfig. 10), and the measures used were: 



1) the greatest breadth of the last whorl from the 

 outer lip of the mouth to the opposite side (a — b), and 



2) the length of the columella projected on the 

 horizontal plane (c— d). 



As will be seen from the figure this latter measure 

 will be a function not only of the absolute length of the 

 columella but also of the "slenderness" of the shell, the 



larger the last whorl in proportion to the whole shell, 

 the shorter is the projection of the columella compared 

 with its absolute length. 



Among the 160 specimens of each sample 60 were 

 selected among the full-grown individuals, while the other 

 100 were taken at random, old and young mixed. Separate 

 tables aud curves (textfig. 11) were made for each of these 

 groups as well as for both groups together. 



In these curves the size-relations of the shells are seen 

 to vary in both samples, but their range of variation is 

 different. The greatest breadth of the shell being in each 

 case represented by the number 10, we find the projection 

 of the length in L. balea varying about a mean of between 

 12 and 12-5, while in L. retroversa the mean is about 11. 



It will further be seen from the same figures, that 

 the difference between the two forms is more conspicuous 



