210 SHELLS AND MOLLUSCOUS ANIMALS. 



Several species of Tellina are also among our 

 common shells, and are generally found with the 

 Donaces buried in the sand, or left by the waters 

 on the shore. Many of them are much thinner 

 and clearer shells than the Donax, and beautifully 

 marked with pale or deep rose-colour, and various 

 shades of purple, yellow, and 

 buff. Our figure represents the 

 common Tellina (Tellina car- 

 naria}, usually called the butter 

 shell, and marked with pale flesh- 

 coloured bands. It is a thicker, 

 firmer shell than most of the 

 genus, and among the most frequent on our sandy 

 shores. 



More highly organized than the inhabitants of 

 bivalve shells, are the univalve mollusks, com- 

 posing the class Gasteropoda. This name refers to 

 the broad expansion on the under part of the body 

 of the animal, which is called a foot ; and the snail, 

 as it creeps over our plants, makes use of this 

 organ, and exhibits its form to us. The Gastero- 

 poda is a large class, including not only the 

 univalved shell-fish, but a number of animals, 

 which, like the slug, have not a calcareous habita- 

 tion. The mollusk of this class is far more 

 symmetrical in form than that of the Conchifera. 

 It has a clearly marked face, with two or four 

 tentacula, like the horns in the snail, which have 

 either eyes at the summit, or, as in most of those 

 belonging to the sea, at the base of these organs. 

 Zoologists arrange this class into several orders, 

 according to the form and situation of the gills 

 by means of which they breathe. Those which 

 breathe air, like the snail, have a delicate network. 



