14 PLANT- ANIMALS [OH. 



The habitat of C. roscoffensis is restricted and 

 localised (Fig. 1). This gregarious species occurs 

 within a well-defined zone of the foreshore of sandy 

 beaches of Normandy and Brittany. Elsewhere it is 

 unknown. 



An observer, walking at low tide seaward across 

 a golden beach in Brittany, passes scattered granite 

 rocks scantily clad with yellow-brown patches of 

 seaweed adventuring landward and before he reaches 

 the main belt of brown seaweeds, some yards land- 

 ward of the thin line of green Cladophora which lies 

 bleaching in the sun, he may see dark, spinach-green 

 glistening patches the colonies of C. roscoffensis. 

 He must tread softly lest the patches melt away 

 at his approach. The colonies may extend for 

 many yards as dark green, irregular strips running 

 more or less parallel with the shore-line, or they may 

 consist of apparently disconnected patches varying in 

 size from an inch or so to a yard or more across. From 

 the intervals between the colonies, the animals are 

 not absent. Though they are not to be seen, they 

 may be smelt. Sand from a part of this roscoffensis 

 zone where no animals are visible, when squeezed 

 between the fingers, emits from the crushed, occasional 

 Convolutas contained in it a pungent and evil smell. 

 The odour, which is like that of decaying fish, is due 

 to the volatile trimethyl amine which is produced 

 by the animal. 



