140 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



7 had no adherent ova masses. 



3 



?? 



1 



4 



?? 



2 



3 



?? 



3 



1 



« 



4 



It was difficult to enumerate the number of ova per mass, on 

 account of their dense coating of sand grains, and the tenacity 

 with which they adhere to the gelatinous envelope. Twelve 

 embryos were visible in one, but the full number is probably 

 somewhat greater. Professor Herdman suggests that the 

 species has acquired the habit of depositing ova upon its 

 neighbours' shells as being the only comparatively stable basis 

 available upon these sands. 



This little species buries itself as soon as the sand or mud, 

 upon which it usually crawls, commences to dry, and on sunny 

 or windy days its presence can be detected only by the presence 

 of numerous small holes. The same behaviour was noted 

 during severe frost in February, 1919 (Ynyslas) when not a 

 single living specimen could be seen upon the surface. 



Littorina littqrea and L. rudis may be met with at times 

 crawling on the firmer sands. These two species, and Mytilus 

 edulis, manage to live on these otherwise unsuitable localities 

 in a manner I have previously described.* Scattered over 

 the surface of certain parts of the beds are clusters composed 

 of one or more mussels fixed to either dead shells, or to one or 

 more living cockles, which act as anchors. Upon the cockles, etc. , 

 may grow trailing tufts of Enteromorpha, and clinging to the 

 mussels are generally several L. littorea and L. rudis. Within 

 the mass and among the byssal threads are frequently to be 

 found one or more specimens of M. balthica. Often a dozen 

 individuals belonging to five species of Mollusca are involved 

 in these clusters — in addition, the common Balanus may be 

 attached also. The little Tornatina (Utriculus) obtusa 



* Journal Marine Biol. Assoc, X, 1. 1913. 



