CHAPTER XXXVII: THE HORN SHELLS 



Family CERiTHiiDyE 



Shell spiral, much elongated, of many whorls, surface 

 tuberculated; aperture channeled in front; operculum horny, 

 spiral ; the head bears short muzzle, slender tentacles and stalked 

 eyes. A large family of tropical and sub-tropical mollusks, 

 living on rocks or among marine vegetation. A few forms live 

 in brackish and fresh water. Some spend much time out of 

 water, on stems of marsh plants. 



Genus CERITHIUM, Brug. 



Shell turreted, imperforate, varices indistinct; aperture 

 small, with short posterior canal, the longer, anterior one oblique; 

 outer lip expanded ; inner lip thickened, concave. Siphon short ; 

 body grooved, truncated in front, narrowed behind; foot secretes 

 a thread by which body may be suspended. It is often attached 

 to a piece of floating seaweed. When unattached the mollusk 

 crawls quickly along by its slender, extensible foot. It emits 

 a green fluid when disturbed. It feeds on all sorts of decaying 

 organic matter, even the slime of snails. Fossil species, near 

 five hundred. C. giganteum, an Eocene fossil, is two feet long. 

 American representatives few and of small size. Marine or 

 amphibious mollusks in tropical seas, with a few in temperate 

 waters. In the West Indies they swarm in great numbers and 

 variety. One species is the sole food of flamingoes after they 

 attain adult size. One sweep of a hand-net in the tide pools at 

 low water on the reefs just out of Key West will gather in hundreds 

 of them, particularly of the species septem-striatum, Say. There 

 are hundreds sunning themselves on every exposed rock. 



The Brown Horn Shell (C eburneum, Brug.), about i inch 

 long, has strong spiral ribs set with rounded knobs, the middle 

 ridge bears the largest. Fine spiral striae and occasional varices 



179 



