HABITS AND ECONOMY OP THE MOLLUSCA. 131 



microscopic plants, brought to them by the current which their 

 ciliary apparatus perpetually excites ; such, too, must be the 

 sustenance of the Magilus, sunk in its coral bed, and of the 

 Calyptroea, fettered to its birth-place by its calcareous foot. 

 Fresh-water bivalves, Sphserium, Unio, are known to have a 

 liking for decaying animal food ; the former being frequently 

 found attached to it, the latter often burrowing in the putrescent 

 mass. 



The carnivorous tribes prey chiefly on other shell-fisli, or on 

 zoophytes ; since, with the exception of the cuttle-fishes, their 

 organization scarcely adapts them for pursuing and destroying 

 other classes of animals. One remarkable exception is the 

 Testacella, which preys on the common earth-worm, pursuing it 

 in its burrow. 



Most of the siphonated univalves are animal-feeders ; the 

 carrion-eating stromb and whelk consume the fishes and other 

 creatjLires, whose remains are alwaj^s plentiful on rough and rocky 

 coasts. Many wage war on their own relatives, and take them 

 by assault ; the bivalves may close, and the operculated nerite 

 retire into his home, but the enemy, with rasp-like tongue, armed 

 with siliceous teeth, files a hole through the shell — vain shield 

 where instinct guides the attack 1 Of the myriads of small shells 

 which the sea heaps up in every sheltered '^ ness," a large 

 proportion will be found thus bored by the whelks and purples ; 

 and in fossil shell-beds, such as that in the Touraine, nearl}^ half 

 the bivalves and sea snails are perforated — the relics of ante- 

 diluvian banquets. The perforation is always made at a point 

 covering the essential organs of the victim. In the acephala it 

 is found at the central part of one valve, usually near the beaks, 

 in the encephala about the middle of the length of the shell. 

 Boring mollusks are a veritable plague to the owners of oyster- 

 banks : the Murex erinaceus in Europe, the Urosalpinx cinerea 

 on the Atlantic and the Purpura crisjyata on the Pacific coasts 

 of the United States are enemies upon whom the oyster-fisher 

 wages constant warfare. The carnivorous gastropods often pay 

 the penalty which they inflict, and not unfrequently the shell of 

 the Natica duplicata may be found, bored through at a spot 

 where its late inhabitant was powerless to repel the intruder. 



There are certain carnivorous genera among the terrestrial 

 gastropods: these are (besides the Testacella), Daudebardia, 

 Grlandina, Ennea, Rhytida, etc. They live on small species of 

 the herbivorous genera. Helix and Bulimus which they detach 

 from their shells by means of their tongues. Sometimes they 

 swallow both shell and proprietor ; as Fischer found an Opeas 

 intact in the stomach of a Glandina. A number of usually 

 herbivorous species of terrestrial mollusks have developed 

 carnivorous instincts when imprisoned with other species. 



