144 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 







Table I. 













Relation of Dorso-ventral diameter (depth) to growth lines, in 500 C. edule. 

 8.8.1919. Bardsea. 





Shell Groups. 



No. of Shells. 



Number of Grooves. 





4 



3 



2 



1 







1 

 2 

 3 

 4 

 5 

 6 



-1-00 cm. 



1-00 to 1-50 cm. 



1-50 to 2-00 cm. 



2-00 to 2-50 cm. 



2-50 to 3-00 cm. 

 + 3-00 cm. 



1 



80 



194 



102 



119 



4 



2 

 6 

 1 



4 



56 

 3 



1 



2 



43 



54 



16 



70 



42 



3 



1 



63 



122 



11 







500 



9 



63 



100 



131 



197 



Differences in their number and distinctness occur in different 

 samples, owing to varying rates of growth, due to variations in 

 food supply, such food supply being in my opinion connected 

 with (1) the situation of the growing cockle within tidal range, 

 (2) its situation with regard to currents, (3) the type of medium 

 (mud, sand, etc.), (4) temperature, (5) spawning period 

 (possibly). 



The age grooves vary in number in my experience from 

 one to eight ; this latter in a " giant " shell from Solva in 

 Pembrokeshire. The whole matter requires investigation, 

 together with (1) the correlation of shell form (as indicated 

 by series of measurements) with the environmental factors ; 

 (2) the similar correlation of density of the population of a 

 given area with such features as the amount of organic matter 

 present within the medium (soil) and a thorough examination 

 of the life history, spawning periods, and development of the 

 cockle. By such means also the reasons for the presence of 

 local " giant " races of C. dule might become apparent. In 

 addition to such beds of exceptionally large cockles as are 

 usually mentioned (Barra),* etc., I have collected a sample 



* Fullarton, J. H., 8th Annual Report Fish. Board of Scotland (for 1889). 

 1890. pp. 211-19. Map. 



