80 



LECTURES ON MOLLUSCA. 



rivers. They are short, stumpy creatures with a rough skin, and 

 closely resemble some of the Sea-slugs. Their eyes are at the end of 

 the stalks, which are not retractile. The teeth are like those of snails, 

 but they have no horny jaws. The breathing hole, vent, and ovary 

 are at the back of the body; the intromittent opening under the right 

 eye. Oncidella has flaps round the mouth. Peronia lives on shores, 

 moving up and down a few feet above tide level. These Slugs have 

 knobs or excrescences on their backs, as well as flaps round the 

 mouth. The British species is said to have the heart in front of the 

 lung, while in all the gther pulmonates it is behind. 



The Veronicella, which lives in damp, shady forests, has a smooth, 

 leathery mantle, and a pair of small, bifid tentacles in addition to the 

 eye-stalks. The ovary opens half way down the side. These Slugs 

 crawl quickly, and are not slimy. They lay their eggs in a coiled 

 necklace. 



TRIBE II. LIMNOPHILA. (Aquatic Snails.) 



The amphibious tribes differ from the true land snails in having no 

 eye-stalks. The tentacles are generally short and stumpy, and the 

 eyes are fixed at their bases, as in the Periwinkles, The tongue-teeth 

 greatly resemble those of the snails. 



Family AURICULID^E. 



The Auriculas were long regarded as sea-shells. They inhabit salt 

 and brackish marshes, and their shells are much more solid than is 

 usual with land-shells. L Some of them absorb the inner whirls like 

 the Nerites. The shells always have narrow mouths, more or less 

 toothed. 



Theytypical Auriculas sometimes have large shells, and increase half 

 a whirl at a time. They have a stumpy spire, long narrow mouth, 

 thickened inside, and a few large folds on the pillar. They rejoice in 

 mud banks in the East Indian archipelago. The animal of Cassidula 

 has the foot cleft behind. The shell is stumpy, and the thickening of 

 the outer lip wrinkled. The shells of Scarabus are conic and rather 

 thin, being adapted to a true terrestrial life. The whirls have two 

 rows of indistinct varices, and the mouth is strongly toothed on each 

 side. The little Alexias represent the previous groups in the Atlantic 

 regions : having a plain and pointed spire. The tiny Carycldum re- 

 sembles Pupa in form, and lives in moist places far oif from the sea. 



The Melampus tribe enjoy sea bathing, though strict air-breathers. 

 Their foot is cleft behind. Their shells resemble Cassidula, but the 

 outer lip is either thin or regularly toothed within. Some species, 

 called Tralia, are said to have a pointed foot. The tentacles in these 

 animals are sharper than in the less aquatic species. The Sandwich 

 Island group Lwmadonta have a curious plait across the outer lip. 

 The shells of Leuconia have a sharp outer lip ; and the animal is said 

 to differ from Alexia in having the foot grooved across. The shells of 

 Pedipes have a very wry mouth like Scarobus, and a very short spire. 

 The animal has a grooved foot, and loops in walking like Truncatella. 



