TURRITELLID.E ; PALUDINA ; PERIWINKLE. 379 



Pelican's foot (Aporrhais), which is found on the British coasts. 

 The Cerithiidae are for the most part of small size ; the shell is 

 elongated and spiral ; and the animal is furnished with a foot of 

 moderate size, which bears a spiral operculum, and with a pair 

 of long tentacles, attached to the sides of which are the short 

 footstalks which bear the eyes. They are found in all parts of 

 the world, generally in the sea, although a few species inhabit 

 fresh water. Of the latter, some even quit the water very fre- 

 quently, and these are capable of suspending themselves from 

 plants by means of glutinous threads. 



994. In the great family of the TURRITELLID^:, the aperture 

 exhibits no trace of a notch, but the form varies greatly from 

 that of an elongated spiral cone to 

 that of a complete disc. The animal 

 has a broad muzzle ; long, slender ten- 

 tacles, at or near the base of which 

 the eyes are generally situated ; and 

 a horny operculum, which is generally 

 spiral, but sometimes concentric. The 

 water is frequently admitted to the 

 branchial chamber by a fold of the 



border of the mantle, representing a rrG . 670 ._ AMPUIjLARI . RUG08A 

 rudimentary siphon ; and in the genus 



Ampullaria, this is much elongated, forming a true siphon. 

 Most of the species are marine, but a considerable number are 

 inhabitants of the fresh waters, especially of warm 

 climates. Of these the Ampullaria (Fig. 670) 

 above mentioned is an example, and another, the 

 Paludina vivipara (Fig. 671), is common in this 

 country. This animal, in common with the other 

 species of its genus, is remarkable for producing 

 its young alive, the eggs being hatched within 

 FIG. 671.-SHELL tne ov id uc t. Of the marine species, the best- 



or PALUDINA. t . 



known is the common Periwinkle, ot which such 

 quantities are used as an article of food in the countries in which 

 it abounds. It is considered in Sweden to afford a sign of the 

 coming weather ; the peasants having observed that, whenever 



