262 MANUAL OF THE MOLLUSCA. 



shelly, witli a flexible border ; slightly toothed on its straight 

 edge. 



Animal Y^ke nerita ; lingual teeth ; median ^ minute ; laterals 

 3, 1 large, sub-triangular 2, 3 minute ; uncini about 60, first 

 very large, hooked, denticulated ; the rest equal, narrow, hooked, 

 denticulated. 



The neritinso are small globular shells, ornamented with a 

 great variety of black or purple bands and spots, covered with a 

 polished horny epidermis. They are mostly confined to the fresh 

 waters of warm regions. One species [N. fluviatilis) is found in 

 British rivers, and in the brackish water of the Baltic. Another 

 extends its range into the brackish waters of the North American 

 rivers ; and the West Indian N. viridis and meleagris are found 

 in the sea. 



''N. crepidularia has a continuous peristome, and approaches 

 navicella in form ; it is found in the brackish waters of India. 

 N. corona (Madagascar) is ornamented with a series of long 

 tubular spines. 



Distrihution, 111 species. West Indies, Norway, Britain, 

 Black Sea, Caspian, India, Philippines, Pacific, West America. 



Fossil, 20 species. Eocene — . Britain, Prance, &c. 



Nayicella, Lam. 



Etymology, navicella, a small boat. 

 Type, N. porcellana. PL IX., Fig. 41. 



Shell, oblong, smooth, limpet-like ; with a posterior, sub- 

 marginal apex; aperture as large as the shell, with a small 



Fig. 113. Navicella. ("Wilton.) 



columellar shelf, and elongated lateral muscular scars; oper- 

 cultim very small, shelly. 



Distribution, 33 species. India, Mauritius, Moluccas, Aus- 

 tralia, Pacific. 



Navicella inhabits fresh waters, adhering to stones and plants. 



Median tooth small ; laterals 3, first large, trapeziform, 2, 3, 

 minute ; uncini numerous, first large, strong, and opaque, the 

 rest slender, translucent, with denticulate hooks (Fig. 113). 



