TUB ULIBRANCHIA TA. 



213 



from that of the young. Some species belonging to this carnivorous genus 

 are also remarkable for their great size, as, for example, the common Conch- 

 Shell (S trombus gigas) of the West Indies, valued as a chimneypiece orna- 

 ment on account of its striking appearance and the beautiful rosy hue of its 

 interior. 



ORDER TUBULIBRAXCHIATA.* 



In this Order of Gasteropods the shell takes the form of a tube, 

 more or less irregular in its shape, but always presenting a spiral 

 contour near its commencement. These tubes very much re- 

 semble those of 

 certain Annelidans 

 (Serpulce) t with 

 which they were 

 long confounded. 

 They are generally 

 found entwined to- 

 gether, and mixed 

 up with coral beds. 

 As the included 

 animals are thus 

 fixed, they have no 

 foot ; but that part 

 of their bodies, 

 which, in ordinary 

 Gasteropods, con- 

 stitutes the tail, is 



bent forward until it reaches beyond the head, where it swells out 

 into a protuberance furnished with a thin operculum ; this serves 

 as a door wherewith to close the entrance of the tube when the 

 animal retreats into its shelter. The head of these Mollusks is 

 provided with two tentacula of moderate size, at the bases of 

 which the eyes are situated : the mouth is a simple vertical slit. 

 (Fig. 224). 



ORDER ScuTiBRAxcmATA.f 



The animals belonging to this Order have their shells very 

 widely open, and frequently not at all spiriform, so that they 

 cover the back, as it were, with a broad shield. 



The Sea-ears (Haliotis] are the most beautiful and richly ornamented of 



* Tubulus, a tube; branchiae, gil's: titbc-gilled. 

 f Scutum, a s hidd ; branchuv, gi.L : shifliied gitts. 



FIG. 224. VERMETTS. 



