348 



LOWER INVERTEBRATES. 



B'lG, 451. — Potamides 

 telescopium. 



and ponds. The species of Cerithium are numerous and variable, and it is said that 

 it was the diflSculty of classifying the species of this genus that first led Lamarck to 

 speculate upon the origin of species. Our species are mostly placed among the sub- 

 genera Cerithiopsis, Jiittium, and Triforis. They are all marine. The species of the 

 latter have reversed shells, and one {T. nigrocinctus) is abundant 

 on bottoms where the algae are numerous. 



The fresh and brackish water species are mostly placed in the 

 genus Potamides, of which Pjjrazus, Telescopiimi, and (Jerithidea 

 are to be regarded as sub-genera. The fifty known species are 

 mostly from the eastern hemisphere. The brackish-water species of 

 the East Indies frequently leave the water and climb on the roots 

 and branches of the mangrove trees, suspending themselves by glu- 

 tinous threads. The Malays are fond of P. telescopium and P. 

 palustre, which they cook by throwing them on their wood fires. 

 The bent pin, so useful (according to Dickens) in extracting the 

 meat of the periwinkle, would here avail but little, on account of the 

 numerous whorls ; so the natives break off the apex of the shell and 

 then suck the animal through tlic opening thus made. The individ- 

 uals of this genus are very numerous in suitable places, and near 

 Calcutta Potamides telescopium is so abundant that the shells are 

 gathered and burned for lime, the anim;ils being previously killed by exposure to the 

 sun. 



The cowries, or porcehiin shells, are known in scientific nomenclature as the Ctp- 

 E^iD^. Like the cones, they are favorites with collectors, and a drawer filled with 

 their enamelled and brightly-colored 

 shells is a beautiful sight. By char- 

 acters derived from the shell they are 

 readily distinguished from all other 

 molluscs, for the spire is nearly or 

 quite concealed by the body whorl. 

 The aperture is long and narrow, ter- 

 minating at each end in a notch, while 

 the lips are usually toothed, the outer 

 one being thickened and rolled in- 

 wards in the adult, though in the 

 young it is thin and sharp, and the 

 spire is visible. The animal has a 

 broad foot, while the mantle is ex- 

 panded on either side so as to form 

 broad lobes (usually fringed on the 

 margin), which turn up over the shell. 

 When full grown these lobes secrete the shining enamel which covers the entire ex- 

 terior of the shell and obscures the spire. The line where the lobes of the mantle 

 meet upon the back is usually marked with a lighter line. 



The princiiial genus, Cyprcea, contains about two hundred tropical and semi- 

 tropical species, only a few of which occur in the Atlantic, the great majority being 

 from the East Indies and the islands of the Pacific. In habit some are retiring, hid- 

 ing themselves under stones and among the branches of coral, while others crawl 



Fig. 452. — Cypraa argus, eyed cowry. 



