GASTEROPODA. 4 



NERITA, L. Nerite. 



Etym. Nerites, a sea-snail, from nereis. 



Type, N. ustulata, PL IX., fig. 35. 



Shell thick, smooth or spirally grooved ; epidermis horny ; outer lip 

 thickened and sometimes denticulated within ; columella broad 

 and flat, with its inner edge straight and toothed; operc. 

 shelly, fig. 86. 



Distr., 116 sp. Nearly all warm seas. W. Indies, Red 

 Sea, Zanzibar, Philippines, Australia, Pacific, W. America, 

 (Cuming). Fig. 86.* 



Fossil, 60 sp. Lias . Brit. &c. The palaeozoic nerites are referred by 

 D'Orbigny to turbo, natica, &c. N. haliotis is a pileopsis. 



Sub-genera. Neritoma, Morris, 1849. N. sinuosa, Sby. Portland stone, 

 Swindon. (Mus., Lowe). Shell ventricose, thick; [apex eroded; aperture 

 with a notch in the middle of the outer lip. Casts of this shell are common, 

 and exhibit the condition of the interior characteristic of all the nerites ; it 

 was probably fresh- water. 



Neritopsis, Grateloup. N. radula, PI. VIII., fig. 9. Shell like nerita ; 

 inner lip with a single notch in the centre. 



Distr., 1 sp. Pacific. Fossil, 20 sp. Trias ? Brit., France, &c. 



Velates, Montf. N. perversa, Gm. PL IX., fig. 36. Inner lip very 

 thick and callous ; outer lip prolonged behind, and partially enveloping the 

 spire. 



PILEOLTJS, (Cookson) J. Sowerby. 



Etym., pileolus, a little cap. 



Type, P. plicatus, PL IX., fig. 37, 38. 



Shell limpet-like above, with a sub-central apex ; concave beneath, with a 

 small semi-lunar aperture, and a columellar disk, surrounded by a broad con- 

 tinuous peristome. 



Distr., marine ; only known as fossils of the Bath oolite, Ancliffe, and 

 Mmchinhampton, 3 sp. P. neritoides is a neritina. 



NERITINA, Lam. Fresh-water nerite. 



Examples, N. zebra, PL IX., fig. 39. N. crepidularia, PL IX., fig. 40. 



Shell rather thick at the aperture, but extensively absorbed inside ; outer 

 lip acute ; inner straight denticulated ; operc. shelly, with a flexible border ; 

 slightly toothed on its straight edge. 



Animal like nerita ; lingual teeth ; median, minute ; laterals 3, 1 large, 

 sub-triangular, 2, 3, minute ; uncini about 60, first very large, hooked, denti- 

 culated ; the rest equal, narrow, hooked, denticulated. 



The neritinse are small globular shells, ornamented with a great variety 

 of black or purple bands and spots, covered with a polished horny epidermis 



* Fig. 86. Operculum of N. peloronta. W. Indies. 



