Ill ENEMIES OF SLUGS AND SNAILS 59 



in their mandibles, and then, throwino- their head backwards, 

 break the sliell by striking it against their prothorax. 



The common water beetle, Dytiscus marginalis, from its 

 strength and savage disposition, is a dangerous enemy to fresh- 

 water Mollusca. One Dytiscus, kept in an aquarium, has been 

 noticed to kill and devour seven Limnaca stagnalis in the course 

 of one afternoon. The beetles also eat L. peregra, but apparently 

 prefer stagnalis, for when equal quantities of both species were 

 placed within their reach, they fixed on the latter species first.^ 



In East Africa a species of Ichneumon {Herpestes fasciatus) 

 devours snails, lifting them up in its forepaws and dashing them 

 down upon some hard substance.- In certain islands off the south 

 coasts of Burmah, flat rocks covered with oysters are laid bare at 

 low tide. A species of Monkey {Macams cynomolgus) has been 

 noticed to furnish himself with a stone, and knock the oysters 

 open, always breaking the hinge-end first, and then pulling out 

 the mollusc with his fingers.^ 



The walrus is said to support himself almost entirely on two 

 species of Mya {truncata and arenaria), digging them out of the 

 sand, in which they live buried at a depth of about 1^ feet, with 

 his powerful tusks. Whales swallow enormous numbers of pelagic 

 molluscs {Clio, Limacina), wiiich are at times so abundant in the 

 Arctic seas, as to colour the surface for miles. Many of the 

 larger Cetacea subsist in great part on Cephalopoda ; as many as 

 1 8 lbs. of beaks of Teuthidae have been taken from the stomach 

 of a single Hyperoodon. 



Fish are remarkably partial to Mollusca of various kinds. 

 The cat-fish (Ghimaera) devours Pectunculus and Cyprina, crush- 

 ing the stout shells with its powerful jaws, while flounders and 

 soles content themselves with the smaller Tellina and Syndosmya 

 which they swallow whole. As many as from 30 to 40 speci- 

 mens of Buccinum undatum have been taken from the stomach 

 of a single cod, and the same ' habitat ' has been recorded for 

 some of the rarer whelks, e.g. Bucc. humphreysianum, Fusus 

 fenestratus, the latter also occurring as the food of the haddock 

 and the red gurnard. No less than 35,000 Turtonia minuta 

 have been found in the stomach of a single mullet. Nudibranchs 

 are no doubt dainty morsels for fish, and hence have developed, 



1 .1. W. Williams, Science Gossip, 1889, p. 280. - Noack, Zool. JB. ii. p. 254. 

 3 La Nature, xv. (2) p. 4G. 



