LECTURES ON MOLLUSCA. 225 



resembles it in form, with swelling whirls, and circular expanded 

 mouth. Iberus is a common group in the Mediterranean region, also 

 found in California ; flattened, often keeled, with the mouth bent down- 

 wards. Ochthephila abounds in the Canaries, with the lip continued 

 all round, as in Caracolla. Hygromia contains the small, flat, umbili- 

 cated snails of temperate regions, with sharp, rounded mouths, thickened 

 within. 



The Helicetta tribe have the margin quite sharp, and the shell thin 

 and glossy. They live in dark, damp places, and are remarkable for 

 the lingual teeth being pointed at the sides. The shells of Discus 

 resemble them, but are not glossy. Those of Zonites are rough above 

 but glossy below. The curious Jamaican group Sagda has a stumpy, 

 elevated shell, with many whirls, and laminae running along the inside 

 of the base. Pitys is angular, with the mouth variously toothed. The 

 shells of Stylodonta have the pillar twisted like AcJiatinella ; and those 

 of Streptaxis have the pillar curiously distorted. 



The Bidimus group are like snails drawn out into an oval, the spire 

 being raised, and the mouth longer than broad. There is generally a 

 plait or fold on the pillar. The typical Bidimi of South America are 

 six inches long when adult, and an inch when born. Their eggs 

 resemble a pigeon's. The animals are exactly like those of the typical 

 snails. Cochlostyla is a Philippine group, with the mouth somewhat 

 rounded and passing into Helicostyla. The shells of Orthalicus are 

 thin, with a sharp lip ; those of Bulimulus approaching Pupa in form. 

 The Partulas are an ovoviviparous group, living on low bushes near 

 the sea in the Pacific islands. Otostomus is a South American group, 

 with very long narrow mouths. The shells of Odontostomus are curi- 

 ously toothed, like Pupa; and Tomigerus has a wry mouth, twisted 

 upwards as in Anostoma. The shells of Cochlicetta are many whirled, 

 like Cylindrella. Chondrus has a tooth close to the suture. Zua is 

 glossy like Helicetta. Azeca resembles it, with a ringent mouth. The 

 shells of Bostryx have the last whirls separated, as in Vermetus. 



The Achatina group resemble Orthalicus, with the bottom of the 

 pillar truncated like Melanopsis. The typical species are African, and 

 are the largest land shells known, being eight inches long. Limicola- 

 ria forms a transition to Orthalicus, with the pillar pinched, not trun- 

 cated ; and Pachyotis, a group which lingers in the islands of the South 

 Atlantic, forms a similar transition to Odontostomus. The West Indian 

 group Pseudotrochus has a porcellanous, highly painted shell. The 

 group Columna is many-whirled, like Cochlicetta. The little Cionellas 

 are glossy, and scarcely truncated. Spiraxis has the pillar bent; and 

 the large group AcJiatinella, which culminates in the Sandwich islands, 

 and is ovoviviparous like Partula, has a sharp, twisted fold on the 

 pillar, instead of a truncation. Tornatellina nearly resembles it, but 

 with additional plaits. 



The Chrysalis snails are remarkable for being narrowed at each end. 

 They are all rather, and some extremely small, and have many whirls. 

 The foot is very short ; and the true tentacles very small or altogether 

 wanting. The Pupas are very stumpy shells, generally ribbed outside; 

 and with the mouth often curiously distorted by plaits. 



In the animals of the little wry-mouthed Vertigo, the tentacles can- 

 15 



