THE SNAIL TRIBE 



3321 



The animals of the genus Planar bis are small, and have the vital organs on the 

 left side. The tentacles are slender as in Physa, but there are no lateral mantle 

 lobes. The shells are all very similar, being sinistrally and spirally coiled up 

 like a rope, in the same plane. They frequent stagnant pools and ditches, or 

 slowly running water, in all parts of the world. The well-known P. corneus is 

 not only by far the largest of the eleven British species, but also larger than any 

 other known form, although some of the South- American types approximate 

 closely. When disturbed, it emits a purple-colored fluid, probably as a means of 

 defense. 



In Physa the animal is always sinistral, having the respiratory and genital 

 orifices on the left side. The tentacles are cylindrical, and the eyes are at their 

 inner base, as in Limncza. The mantle is furnished on each side with more 01 less 

 elongate lobes, which, when the mollusk is crawling, are folded back upon the 

 exterior of the shell. In their habits these snails resemble the preceding genus, and 

 they are almost cosmopolitan in 

 their distribution. Physopsis, a 

 Central- and South-African 

 form, has a reversed shell like 

 Physa, but is distinguished by 

 having a tooth or fold on the 

 columellar margin of the aper- 

 ture. In Chilina the shell is 

 dextral, like that of Limntza, 

 but differs in being covered 

 with a periostracum, and ex- 

 hibiting reddish wavy color 

 markings. The columella is 

 thickened and furnished with 

 one or more folds or plaits. 

 They are found only in clear 

 running streams of South 

 America. 



The curious pulmonate 

 known as Amphibola some- 

 what resembles a periwinkle 

 in form. It lives between tide 

 marks in brackish or salt 

 water, on mud flats at the 

 mouths of rivers in New 

 Zealand, and is used as food 

 by the natives. It is abundant 

 in some places, and is a slug- 

 gish creature, subsisting upon 

 the vegetable matter contained 

 in the mud, large quantities RAMSHORN SNAIL (Planorbis corneus'). 



