The Horn Shells 



times cover the trunks of marsh trees in Natal so thickly that not 

 an inch of the bark is unoccupied. A naturalist who collected 

 them at this station says that the mollusks are attached by a 

 trifle of brittle mucus that affixes the lip to the tree. None hangs 

 by a thread. 



Habitat. — Madagascar and India. 



C. scalariformis, Say, resembles a staircase shell (Scala), 

 as its whorls are crossed by a multitude of distinct longitudinal 

 riblets. It is an inch long, whitish to chocolate-coloured. In the 

 dark shells the ribs are white. It habitually crawls up grass 

 stems, and stays most of the time out of water. 



Habitat. — Florida. 



Genus POTAMIDES, Bron. 



Shell imperforate, turreted, angled, tubercled or spiny, with 

 thick epidermis, apex often decollated; operculum horny; foot 

 nearly circular, blunt behind; siphon fringed. A genus of tropical 

 brackish water species which are able to live for long periods 

 suspended above the water by threads spun from the foot. 



A species, P. palustris, Brug., lives in the salt marshes 

 of the Eastern Archipelago. The natives collect these in quan- 

 tities for food. They are roasted, then the contents of the shell 

 are sucked out, the spire being broken off first. 



In Borneo the large P. telescopium, Brug., 8 to lo inches 

 long, is an article of food. Near Calcutta this species is so 

 abundant that the shells are burned for lime. The live mollusks 

 are first heaped in the sun to die. 



P. sacrata, Gld., has a narrow, dark brown spire, with 

 rounded whorls marked with spiral ridges and crossed by longi- 

 tudinal ridges and occasional stronger varices. It is abundant 

 on muddy flats at low tide. Length, i to i^ inches. 



Habitat. — California. 



Genus BITTIUM, Leach 



Shell elevated; whorls many and granular, with irregular 

 varices; anterior canal short, not recurved; outer lip not reflected, 

 usually with an exterior rib; foot narrow, square in front. Small 

 mollusks, in temperate seas. 



i8i 



