MOLLUSCA. 89 



genus in which the shell is somewhat ear-shaped, and the foot very large 

 and thick, nearly hiding the shell, which is sunk into it. The tentacles are 

 flat and triangular, but unaccompanied by eyes. Although the animal is 

 too large to enter the shell, it is provided with an operculum. Natica {N. 

 canrena^ pi. 'io,fig. 88) is carnivorous like the preceding genus, and like 

 it, has no siphon. It has a large foot (four or five times the length of the 

 shell) bearing an operculum. The head is terminated by a pair of lips from 

 which a rostrum can be protruded. 



Order 11. Pneumonobranchia. This order includes all the spirivalve 

 and naked mollusca, whether inhabiting land or water, in which the branchiae 

 without being proper lungs, are adapted for breathing air, so that the species 

 which inhabit the water are obliged to come to the surface from time to 

 time to breathe air. They seem all to be phytophagous. The order includes 

 eight families. 



Fam. 1. Amjmllariidw. The genus Ampullaria has a globular shell 

 several inches in size, which is generally covered with a green periostraca, 

 and is provided with a closely fitting concentric operculum, which is in 

 some cases corneous, and in others shelly. AVith Paludina and Yalvata it 

 forms one of Lamarck's families, named Peristomata by Keeve. The North 

 American species is figured with the animal in the monograph already 

 quoted. The head is proboscidiform, the extremity cleft, leaving a conical 

 branch half an inch long on each side, and these are used as palpi. The 

 mouth is purse-shaped, the tentacles slender, tapering, and more than an 

 inch long, the eyes borne upon a secondary tubercle at the base externally. 

 The shell is without a notch, yet there is a siphon an inch long which is 

 formed by an extension of the mantle folded into a tube. This is brought 

 to the surface of the water and air drawn through it, and often expelled 

 from it in bubbles when beneath the surface. Guilding describes a shorter 

 siphon upon the right side. The animal lives in the rice swamps of Georgia, 

 feeding upon living plants. Living mostly in the intertropical regions of 

 both hemispheres, where the waters frequently disap]-jear in the dry season, 

 Ampullaria has the power of becoming torpid beneath the mud until the 

 return of the wet season. Some specimens sent from Egypt to France 

 were thrown into water to clean them, and the next day they were found 

 moving about. Deshayes dissected some of these, and found pectinated 

 branchiae, which would ])lace the genus near Paludina, and he describes a 

 large cavity, to which he assigns the function of holding a store of water to 

 be supplied to the branchia; during the period of torpidity. This may be 

 correct; although a further examination will probably show that this cavity 

 is adapted to breathe air, and on this account we place it in the present 

 order. Planorhis hicarinatus (and probably its entire family) hybernates 

 at the bottom of streams with the air cavity filled. The ability to breathe 

 air and water by means of distinct organs is not anomalous, as it appears in 

 certain reptiles. The sexes are separate. 



Fam. 2. Am.phiholidce. Tlie genus Am2?hibola (also named Ampidlacera) 

 has a sub-spiral corneous operculum, and is formed upon a New Zealand 

 shell formerly considered to be an Ampullaria. It was found to breathe air 



293 



