MoLLUSCA OF British Guiana. 43 



is discoidal, the coils taking place in one plane. They 

 have been obtained from the ponds on the savannahs of 

 the interior. In A. peristomata, in which the shells are 

 ventrlcose, the surface markings are linen-like. 



The true Snails, the Pond-snails and the Slugs, are 

 easily distinguished by their breathing air dire6lly in a 

 pulmonary chamber, formed by a folding of the mantle — 

 similar in its development to the folding that gives rise 

 to the branchial chamber in the gill-bearing forms such 

 as the Apple-snails — and by the absence of a shelly 

 operculum. 



In Streptaxis, the shell is nearly globular, and the 

 axis of the spire is distorted, that of the lower not agree- 

 ing with that of the upper whorls, and giving an oblique 

 appearance to the shell. The S. deformis, which occurs 

 commonly in moist situations under old rubbish and 

 rotting vegetable matter, has a diameter about equal to 

 that of a common shirt-button. In the young stages, the 

 shells are nearly discoidal and hyaline, being then super- 

 ficially very similar to specimens of Hyalina ; but with 

 the growth of the whorls, the sub-globose condition is 

 reached, and the axis becomes slightly perforated, and 

 the lip thickened. 



In the Lemon-snails (Bulimus) the shells are oblong 

 or turreted, with the margins of the aperture unequal. In 

 Brazil, the large species are eaten, and are said to be sold 

 commonly in the market at Rio. The largest of the Guiana 

 species, B. ohlongiis, is about 4 inches in length, with the 

 peristome thickened and red. No doubt it would make 

 a very palatable food. It occurs plentifully on the 

 savannahs of the interior, in the neighbourhood of ponds, 

 and streams. What its food may be, in its wild condi- 



F2 



