PLANT AND ANIMAL ASSOCIATIONS 51 



L. exigua in Japan (Mitzukuri, 1902). The periwinkle Tec- 

 tarins in New South Wales is stated to withstand the hottest 

 sunshine (Kesteven, 1903), while Melaraphe is described by 

 Hedley(i9i5)as leavingits small rock pools for dry land should 

 conditions in them become unsuitable during neap tides. 



In Cardigan Bay the Littorinidse persist in the areas 

 devoid of Trochidae, the presence of which is apparently 

 correlated with shore drainage and the type of rock or 

 soil from which it flows ; their presence or absence 

 may depend on the lime content of the water. Thus 

 M. crassa can be seen to break zone and follow seaward 

 streamlets flowing from boulder clay. At the mouth of 

 the River Wyre, near Llanrhystyd (and probably else- 

 where), there occurs a curious lateral zoning due to 

 the influence of fresh water in bulk. The spawning 

 habits of the Littorinidae are likewise adapted to their 

 diff'erent life conditions in a most interesting manner, as 

 will be noted elsewhere. Even the coastal and shore fishes 

 are subject to a zonal distribution. In the Plymouth area 

 the Gobiidae have the following distribution. The most 

 estuarine form is Gohiiis microps^ the young occurring in the 

 Sound and even outside the breakwater, while the adults 

 are found in brackish, or frequently nearly fresh water. The 

 black goby (G. Titger) and spotted goby {G. ruthensparri) also 

 occur in estuaries but near the surface, not at the bottom ; 

 the rock goby (G. paganellus) is common under stones at 

 the level of the lowest spring tides, while the freckled goby 

 (G. minutus) never appears to go far from shore. On the 

 other hand, the painted goby (G. pictus) is found in more 

 open water, and G. elongatus and G. jejfreysii are deeper 

 water species (Lebour, 1919). 



The Animal Associations of a Sandy Shore. — Recent 

 investigations of sandy shores and cockle beds on the 

 west coast of Great Britain have brought out not only a 

 distinct zoning, but a very interesting stratification (Walton, 

 1920). Broadly, these strata are : 



1 . Floating and swimming tidal species (Plankton). 



2. Surface-dwelling species, Paludestrina stagnalis, etc. 



