3350 THE MOLLUSKS OR SHELLFISH 



or upon corals. Rhizochilus in early life is like the young of Purpura, but subse- 

 quently it attaches itself to barked corals (Antipathes] , living a prisoner's life, im- 

 mured within its own shell. It prolongs the lips of the shell around the stems of the 

 coral, completely closing the aperture, with the exception of the siphonal end, which 

 it extends into a distinct tube, serving to carry both water to the gill and food to the 

 mouth. What the nature of its nourishment may be possibly derived from iheAntz- 



pathes itself and what may be the reason of 

 this self-immurement, are problems to be 

 solved. Coralliophilamadreporarum attaches 

 itself to corals; other species live a more ac- 

 tive life, crawling over the surface of the 

 coral. Several are tinted with lilac, and have 

 purple apertures; others, however, are en- 

 tirely white. Leptoconchus and Magilus are 

 both dwellers in coral. The former lives in 

 crypts excavated in brain stone corals, and 

 resembles, as regards the shell, the young 

 Rhizochilus antipathum. a. Young; b. Adult, state of the latter. Magilus affects coral 



reefs, and is remarkable for the great altera- 

 tion which takes place in the course of its career. At first it assumes the form of 

 an ordinary spiral shell, and takes up its abode within the crevices of growing 

 coral. The coral slowly advances around the shell, and would soon inclose it, if 

 the mollusks were not provided with some means of defeating this. The creature 

 prolongs the lips of its aperture into a long, but mostly crooked tube, so as to keep 

 pace with the growth of the coral, and keep the tube open for the free ingress of 

 the water. As the tube increases it becomes too long for the animal; consequently 

 the mollusk fills up the spiral portion, and as much of the tube as is not required. 

 These shells are found in the Red Sea, and the Indian and Pacific Oceans. 





 SECTION T^ENIOGLOSSA 



The majority of the mollusks included in this section of Pectinibranchs are 

 marine forms; and although a few families are found in fresh water, while others 

 are terrestrial and air breathers. Typically, the radula has seven rows of teeth, 

 one central, and three laterals on each side; but there are a few families in which 

 this armature is modified. Sometimes there is only a single lateral on each side; 

 but, on the contrary, the number of laterals occasionally reaches five a side. They 

 are curved and claw-like in some groups, but in others merely have serrated edges. 

 Forty-two families are included in this section; but the limits of this work admit 

 only of an account of some of the more important. The animals of one group are 

 provided with shells, which either have a distinct, prolonged anterior canal, or else 

 the aperture is more or less deeply notched at the base. In another group the 

 mouth is entire, without notch or siphonal canal. Some have a retractile proboscis, 

 like murices and whelks; others have a longer or shorter muzzle or rostrum, which 

 is somewhat contractile. 



