SEA-FISHERIES LABORATORY. 143 



NOTES ON THE SHELL OF CARDIUM EDULE. 



By C. L. Walton, M.Sc. 



(Department of Zoology, University College of North Wales, 



Bangor). 



Several writers refer to variability in the form of the shell 

 in Cardium, and have made general statements referring to 

 the relative thickness of shell, its obliquity, and other features 

 to certain physical features of the environment.* 



It is possible that a series of detailed measurements of 

 samples from different beds would show these differences in a 

 definite manner, and some preliminary work has been done. 



One character that has attracted attention is the presence 

 of certain prominent concentric grooves, the number of which 

 has been generally taken to indicate the age of the shell, the 

 grooves denoting periods during which growth has ceased, 

 notably winter. An attempt has been made to test the validity 

 of this belief. These "annual" grooves were found to be 

 especially well marked in a sample recently collected on the 

 Bardsea beds, near Ulverston (Morecambe Bay), in many 

 cases the usually more or less well marked groove being replaced 

 by a " step " separating the shell of one growth period from 

 the next. These cockles occurred on a bank situated fairly 

 high in tide marks, and therefore exposed to marked tem- 

 perature range. 



That these grooves do indicate age with some accuracy 

 seems to me to be borne out by the table appended (Table I), 

 since their number increases in a regular manner along with the 

 increase in size of shell, throughout each given sample. 



* Among these may be mentioned : — 

 Bateson, W., "On some variations of 0. edvU apparently correlated i<> the 

 Conditions of Life." Phil. Trams., Boy, Soc, London (B). Vol. 180. 

 1889. 

 Fullarton, J. H., 8th Annual Report Fishery Board Scotland. 1890. 

 Forbes, E. and Hanley, S., "History of British Mollusoa," II. L853. 

 Jeffreys, .J. Gwyn, " British Conchology," II. IM.'J. 



