312 LIFE BY THE SEASHORE. 



to four inches in length, the greater about six to seven 

 inches; but the former may reach seven inches, the latter 

 twelve to thirteen or more. In both cases the colours are 

 similar, being greenish above with broad lateral silvery 

 bands and a pale under surface, but the silvery gleam is 

 more pronounced in the smaller fish. Further, the latter 

 in proportion to its length is more slender than the larger 

 form, and tapers more rapidly in the anterior region. When 

 once appreciated this is the point most useful in distinguish- 

 ing the two, but till this can be done the distinction may be 

 very readily made in the following way. Draw an imaginary 

 vertical line from the anterior extremity of the dorsal fin to 

 the ventral surface ; in the lesser sand-eel this line will cross 

 the backwardly-directed pectoral fin, which is elongated and 

 pointed; in the greater sand-eel the line passes behind the 

 pectoral fin, which is short and rounded. In both species 

 note that there is only one dorsal and one anal fin, that 

 ventrals are absent, the scales minute, and the whole form 

 such as to render the action of burrowing rapid and easy. 

 The active agent in the process, as already noted, is the pro- 

 truding lower jaw, which is proportionately somewhat longer 

 in the greater than in the lesser sand-eel. 



This short list includes most of the fish common in the 

 rock pools on the North-east Coast, but to the list may be 

 added the flounder, as an example of the exceedingly inter- 

 esting family of flat-fish, which includes in the turbot, brill, 

 plaice, sole, and others, some of our most esteemed food- 

 fishes. Young flounders are usually common in the rock 

 pools, and their many peculiarities of structure render them 

 worthy of careful study. As is obvious from their shape 

 they are ground forms, adapted for life on the bottom. In 

 this respect they resemble the skate and the fishing-frog, but 

 differ from both in the way in which the adaptation is 

 produced. In fishing-frog and skate the surface upon which 

 the animals rest is the under surface a condition which 

 one would regard as the natural one; but in the flat-fish it is 

 one of the sides. In other words, the fish are laterally 

 compressed squeezed, as it were, until the upper and lower 

 surfaces have become sharp edges. Note the results of this. 

 The pectoral fins in an ordinary fish lie at the sides of the 

 body, therefore in the flounder we find one on the upper 



