218 NATURAL HISTORY. 



is oblong, smooth, and white, but without perforation or notch, and is permanently -covered by the 

 mantle of the animal, which is black. It inhabits shallow water under stones. Ten species are 

 described from the Eed Sea, the Philippines, Australia, &c. 



FAMILY XXIII. 



The spire is very small and depressed, the shell is thick and round. The animal absorbs 

 the internal portion of its shell to give i-oom to the soft parts of its body; the aperture is half 

 round, the columella is flattened, the operculum shelly, sub-spiral, and is articulated to the 

 shell by a remarkable hinge-like process. The head of the animal is short and broad, the eye-stalks 

 are prominent, the outside tentacles long and slender ; the foot is oblong and triangular. 



Genus Nerita. The shell has a horny epidermis, a thick outer lip, toothed within, and a 

 broad and flat columella, the inner edge of which is straight and toothed. The Nerites are 

 found in all the warm seas of the globe ; they inhabit the littoral zone. One hundred and sixteen 

 species have been described. 



Genus Neritina. The fresh -water Nerites, like the marine Neritas, have a rather thick shell, 

 with a sharp outer lip and a straight toothed inner one; the operculum is shelly, with a horny 

 border, toothed on its straight side. 



The Neritinse are small globular shells, ornamented with a gi-eat 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 water of North American rivers ; and the West Indian N. viridis and meleagris are 

 found in the sea. (S. P. Woodward.) Another form is found in the brackish waters of India. 

 N. corona (the Crowned Nerite), from Madagascar, is ornamented with a series of long tuber- 

 cular spines. One hundred species are found living, and twenty fossil. " Neritina sulcata is found 

 on the foliage of tall trees, many hundreds of yards from the river's bank in the Celebes." (Adams.) 



The genus Navicella has a smooth, oblong, Limpet-like shell, with a small columella-shelf beneath; 

 the operculum is very small and shelly ; the shell is covered by a dark olive epidermis. The " Boat- 

 shells," as they are called, inhabit fresh waters, adhering to stones and water-plants. Twenty-four 

 species are described. 



FAMILY XXIV. PATELLID^E. 



The Limpets have conical shells, the apex of which is turned towards the front; they have 

 a horseshoe-shaped muscular scar inside. The head is provided with tentacles having the eyes 

 at their outer bases, the foot is as large as the edge of the shell, the gills are concealed at the 

 back of the head, the tongue is ribbon-like and of great length. 



Genus Patella.* In Patella the shell is usually oval and tent-shaped, the interior smooth, 

 but not pearly, the outside rough or having radiating ribs, the margin sometimes spiny. 



The tongue of the Limpet is longer than its shell ; it has 160 rows of teeth, twelve in each 

 row, or 1,920 in all. Patella variegata, two inches and a quarter long, lias a tongue twelve inches and 

 a half long. (Blanford.) The Limpets inhabit rocks between tide-marks, and are left dry twice 

 every day. They adhere firmly like a sucker to the rock, and it is difficult to detach them 

 without breaking their shells. They always return to the same spot after feeding, and the 

 place where they rest, even on very hard rock, is found to be worn into a smooth concavity 

 beneath the foot of the animal, and the margin of the shell exactly fits the inequalities of the 

 surrounding surface. The Limpets are all vegetable feeders. One hundred living species have been 

 described. They are world-wide in distribution. The Patella, or Rock Limpet, is much used by 

 fishermen for bait. On the coast of Berwickshire nearly twelve millions have been collected 

 yearly, until their numbers are so decreased that collecting them has become tedious. In the 

 north of Ireland they are used for human food, especially in seasons of scarcity. Many tons' 

 weight are collected annually near the town of Larne alone. (Patterson.) 



The " Oyster-catcher " (Haematopus ostralegus), a well-known sea-shore bird, does not 

 subsist upon the Oyster, as its name implies, but chiefly upon the Rock Limpet. The adroitness 



* Latin, patella, a dish. 



