198 NATURAL HISTORY OF OUR SHORES 



line " of our marine zoology, but which calls for attention 

 on account of its remarkable habit, is Galeomma Turtonii. 

 This little bivalve mollusc, unlike all its relatives, has 

 more or less the habit of a gastropod. It opens its 

 valves right and left, and crawls, or at least, adheres 

 (for I have not seen it progress) to the rocks, with its 

 foot. It is pure white, and about three - quarters of an 

 inch in length. 



A list of all our shells would be of no interest to the 

 general reader, and the conchologist has, of course, his 

 text-books. 



There are about one hundred and forty species of bivalves 

 on our shores and in the British Channel. 



Allied to the lamellibranchi, but possessing but one 

 valve, in the form of a bent tube of elongated, conical form, 

 and open at both ends, is an order of molluscs termed the 

 Solenoconchia. It is represented on our shores by two 

 species, well known as the " Tusk Shells " (see Fig.). 

 These live, buried in the sand at extreme low water, on pretty 

 well all our shores. The species found here are Dentalium 

 entalis and Dentalium tarentinum. 



The Gastropoda (Fig. 86). These are thus denned : 

 Molluscs, with distinct head often bearing tentacles, a 

 ventral, muscular foot, and undivided mantle, which usually 

 secretes a shell, simple and platelike, conical, or spirally 

 twisted (Glaus). 



They have also a chitinous ribbon set with sharp teeth, 

 which lies in the floor of the mouth. It is termed the 

 radula, or the " tongue," also, erroneously, the " palate." 

 It serves the purpose of rasping or breaking up the food 

 of the mollusc. 



In some of the carnivorous forms it serves as a boring 

 instrument. By the recurving of its end a number of the 

 sharp, siliceous teeth are set in such position that by a 

 semi-rotary movement the hardest shells can be pierced. 



