BASOMMATOPHORA. 415 



lung sac). The generative organs open some way in front, on 

 the right side. 



The Pulmonata are generally terrestrial, sometimes fresh-water, 

 rarely marine. They are cosmopolitan and include about 6000 

 species. They generally become torpid during part of tlt^ year 

 in warm countries in .the dry season (aestivation), in cold in .winter 

 (hibernation). Hibernation in this country lasts about one quarter 

 of the year, and during it the heart beats no more than twice 

 a minute. 



The mouth armature consists of an unpaired, horny upper jaw 

 (which may be absent), and of a radula with a great number of teeth 

 in the transverse row. 



All are hermaphrodite. A few, e.g. species of Clausilia and 

 Pupa, are viviparous. Most lay eggs, either, as in the fresh-water 

 forms on water plants, united in tubular or flat masses, or as in the 

 terrestrial forms in damp places, each one being surrounded by a 

 protecting shell which may be calcareous. The ovum is always 

 embedded in a large mass of albumen, which serves as nourishment 

 for the developing embryo. 



Tribe 1. BASOMMATOPHORA. 



Shell always present and external. There is one pair of non-invaginable 

 tentacles, at the base of which are the eyes. The penis is remote from the 

 female orifice (except in Amphibola and Siphonaria). In Auricula alone among 

 Pulmonates is the hermaphrodite duct not divided ; and, passing from its opening 

 which is anterior to the mantle-opening, there is a groove which is closed in front 

 and leads to the penis. The closed part of this groove lies close beneath a 

 superficial groove in the skin. In Amphibola, Chilina, and the Siphonariidae 

 the duct splits, but the penial and vaginal openings are joined. There is 

 generally a circular osphradium near the opening of the pulmonary cavity, 

 between it and the renal opening. Radula multiserial. Fresh-water or quasi- 

 marine. 



Fam. 1. Auriculidae. Terrestrial, usually maritime. Respiratory aperture 

 behind. Shell spiral. Auricula Lam., found in brackish- water swamps of 

 tropical islands, on roots of mangroves, and by small streams within the 

 influence of the tide ; traces of small anterior tentacles ; Carychium Miiller ; 

 Alexia Lam.; Pedipes Adanson ; Melampus Montf. ; Otina Gray. 



Fam 2. Amphibolidae. Visceral mass and shell spiral ; operculum present. 

 Aquatic, marine. Amphibola Schumacher, shores of New Zealand and Pacific 

 Islands. 



Fam. 3. Siphonariidae. Visceral mass and shell patellifonn ; tentacles 

 atrophied; marine with aquatic respiration. Siphonaria Sow., secondary 

 branchial lamellae on roof of mantle-cavity ; Gadinia Gray, no branchia. 



Fam. 4. Limnaeidae. Fresh-water animals with aerial respiration. Shell 

 variable. Limnaea L. ; L. stagnalis L., pond-sn#il ; Amphipeplea Nillsson ; 



