MOLLUSCS. 



323 



Fig. iul.—rurOo t 



operculum calcareous; the base of the shell is never flattened. The species are 



mostly tropical and littoral, delighting in rocky coasts where they are exposed to the 



force of the waves. In the Orient the larger species 



are eaten. The largest species known is Turbo nuir- 



moratiis of the Chinese Seas. In Delphinula the shell 



is depressed, the aperture round and pearly, the um- 



liilicus open, the operculum horny, and the whorls of 



the shell are usually spiny. The genus is found on tla' 



coral reefs of the Indo-Pacific Seas, near low-water 



mark. Our figure shows the under surface of the shell, 



with the body extended. 



Phasiandla contains species which have somewhat 

 the shape of the genus Bulimus among the pulmonates. 

 The shell is not pearly but is richly colored ; whence 

 the name pheasant shells. About forty species are 

 kuo^\'n, all from tropical seas. Those from Australian and New Zealand seas are large, 

 reaching occasionally a length of about two inches, but those from other parts of the 

 world are smaller, our West Indian forms being very small. Rotella contains a number 

 of brightly-colored depressed species from the eastern seas. In Moiiodonta, which is 

 much like Turho in general appearance, the outer lip is much thickened and grooved, 

 while the columella is toothed. It has about the same distribution as the last species. 

 In the Malay Arehipelago one of the species is ealeu, notwithstanding its peppery 

 taste. 



The Neritid.e contains thick henuspherical shells with a very small spire, a .sharp 

 outer lip and a calcareous operculum which is frequently irreg- 

 idar in shape. The eyes are placed at the extremity of the 

 slender eye-stalks, which arise from the head outside the long 

 and slender tentacles. The foot is broad and triangular, the 

 apex being behind. As the animal grows, it absorbs the inner 

 part of the whorls of the shell, so that the resulting cavity is 

 simple instead of sjiiral. The typical genus is JS/'erita, which 

 has a thick or spirally grooved shell. The columella is much 

 thickened and toothed, and iu one species, W. pdoronta., this 

 is ornamented with a blotch of red, giving the shell the common 

 name of bleeding tooth. Most of the sijecies are marine, but many ascend the streams 

 entering the ocean to such a distance that the water in which they live is brackish. 



Neritina is much like j^erita, but is more globular. The shells are variously orna- 

 mented with spots or bands of black and purj^le laid upon the polished exterior. The 

 species are mostly confined to the fresh waters of the warmer regions of the earth, 

 but some species are found in the sea. N'avicella is more like the slipper limjiets 

 {Crepklula) in appearance, the aperture embracing nearly the entire shell. They are 

 fresh-water forms, and the resemblance to the limpets is strengthened by their mode 

 of life as they attach themselves by their foot to submerged stones aiid plants. 



The family Pleurotomarid^ shows resemblances to both the Trochidaj and the 

 Haliotidae. The shell is much like that found in the latter family, exce]it that the outer 

 lip of the aperture is notched, or there is a series of ]ierforations in the upper part of 

 the whorl. The species are largely fossil, the living forms being few in number and 

 comparatively rare. In most of the species the notch in the aperture of the shell is 



L'olumellar thickenina 



