178 



of breathing. Of our two British species one has been separated as a new 

 genus, Velletia, on account of some minute difference in the tongue- 

 teeth. 



1. capuloides, Jan. 



2. concentricus, D'Orb. 



3. culicoides, id. 



4. fluviatilis, Mutter. 



5. Gayanus, D'Orbiyuy. 



Species. 



6. irroratus, Lamarck. 10. oblongus, Lightfoot. 



7. lacustris, Midler. 11. radiatus, Lamarck. 



8. Moricandi, D'Orbigny, 12. rivularis, Say. 



9. obliquus, Broderip. 13. spina-rosa, Drapnd. 



Figure. 



Ancylus fluviatilis. PI. 18. Fig. 94. Shell, showing its open, Limpet- 

 like form, and sharply incurved top. 



Genus 2. LYMNiEA, Braparnaud. 



Animal ; having a broad head, the tentacles being also broad, with 

 the eyes placed at their inner bases ; mantle sometimes reflected 

 over the shell, foot broad, often oblong. 



Shell ; oblong or ovate, sometimes turriculated, smooth, horny, 

 spire sharp, aperture mostly large, lip simple. 



In this genus are included two very fairly defined groups, known re- 

 spectively as Lyvincea proper, and Jmphipeplea. Of the first, our common 

 British L. stagnalis is a good typical species, the shells being mostly light 

 and largely inflated, though some have a narrow turriculated growth, and 

 are thicker in substance. The second group, of which there are many 

 foreign species not as yet described, is distinguished by an inflated shell of 

 a shorter Bulla-like form, over which the animal, as in that genus, more or 

 less reflects the mantle. 



The Lymncea inhabit ponds, lakes, and cpaiet streams, in all parts of the 

 world, being of a dull uniform horny substance, with little or no variation 

 of colour. 



1. acuminata, Lamarck. 



2. ampla, Mighels. 



3. arapullacea,i?os<s'w.. 



4. appressa, Say. 



Species. 



6. Burnettii, Alder. 



7. catascopium, Say. 



8. columellus, id. 



9. desidiosa, id. 



5. aurioularia, Drapnd. 10. elodes, id. 



11. elongata, id. 



12. emarginata, id. 



13. fragilis, Pulteney. 



14. fusca, Pfeiffer. 



15. gingivata, Goupil. 



