342 LITTORINID^E. 



tudes of climate ; and (what is of more consequence to 

 them) they are supplied all the year round with an 

 abundance of food. It is otherwise with some of their 

 small cousins, the Rissoa, which depend for their sub- 

 sistence on the Zoster a marina or sea-grass. These 

 must either perish, like the greater number of the insect 

 tribe, or remain in a torpid state until 



" To mute and to material things 

 New life revolving summer brings." 



The former supposition is more probable. Homer, 

 with his tendency to view all nature in relation to our- 

 selves, illustrated the idea of such annual reappearance 

 of life by some well known lines, which I will venture 

 to paraphrase. 



Men are like the race of falling leaves, 

 That winds in autumn whirl and sweep away : 

 Yet spring, with joy and freshness ever rife, 

 Nature will soon restore to former life. 

 Each year the same unvaried tissue weaves 

 Of birth and death, of verdure and decay. 



Several species of Littorina abound on every stony 

 part of our coast ; and the seaweeds swarm with different 

 kinds of Lacuna and Rissoa. All live together in perfect 

 harmony ; there is here no " struggle for existence," nor 

 intermixture of races. Similar conditions may reason- 

 ably be presumed to have continued ever since the for- 

 mation of the Crag a period of incalculable antiquity- 

 because we find associated in this formation certain 

 species of Littorina and Rissoa unquestionably identical 

 with those which still inhabit the same area, and even 

 exhibiting a variability of form precisely analogous to 

 what is observable at the present time. The prevalent 

 hue of the animals in the present family (which indeed 

 may be said of the Gasteropoda in general) is yellowish, 



