FAMILY XENOPHORID^E. 



Shell depressed or conical, trochiform, with carinated periph- 

 ery, not nacreous, soldering shells, stones, etc., to its upper sur- 

 face. Operculum large, horny, subannular,'with lateral dextral 

 nucleus, muscular impression sinistral, semilunar, extending the 

 whole length. 



Animal with long, annulate d muzzle, elongated, subulate ten- 

 tacles, with sessile eyes at their external base ; foot small, used 

 for jumping, not walking, with the anterior portion expanded, 

 posteriorly tapering; gill long, composed of narrow laminae and 

 filaments. Dentition, 2-M'l'2; the central tooth subtrigonal, 

 multicuspid, laterals large, subtriangular, the margin reflected 

 and multicuspid, the marginals very narrow and long, arcuated 

 (PL 30, fig. 8). 



These mollusks scramble along like the Strombs ; they extend 

 and fix the front dilated part of the foot, and draw the posterior 

 portion up to it, jerking the shell forwards at every movement ; 

 this mode of progression is adapte.d to the nature of the surface 

 on which they move, which is usually composed of the debris 

 of dead shells. The shell resembles a Trochus, but the texture 

 is not nacreous. The peculiarity of this tribe is the habit of 

 agglutinating foreign bodies to the upper surface of the shell, 

 which is carried to such an extent in some instances as to con- 

 ceal the volutions and give the structure the appearance of a 

 small pile of fragments of stones and shells. That this imitation 

 of its surroundings is protective in its nature, there can be no 

 doubt ; but in some of the species the protection is not apparent, 

 the agglutinating process being restricted within narrow bounds, 

 or sometimes not developed, and when exhibited is confined to 

 a single row of small bivalves or stones on the suture or periph- 

 ery, arranged with a degree of regularity as to size, and occur- 

 rence indicating the existence of choice or artistic taste on the 

 part of the mollusk. Of the shells attached, single valves of 

 lamellibranchs are preferred, probably because they give more 



(150) 



