171 



Species. 



1. alpestris, Shuttleworth. 5. obtusa, Pfeiffer. 9. spirorbis, Draparnaud. 



2. cristata, Alder. 6. Pupoidea, Gould. 10. tricarinata, -Say. 



3. Cumingii, Reeve. 7. pygmea, C. i?. Adams. 11. trochlea, Bunker. 



4. depressa, C Pfeiffer. 8. sincera, #0^. 



Figure. 



Valvata Cumingii. PI. 17. Fig. 88. Shell, showing a rather more de- 

 pressed form than is usual in this genus. 



Genus 4. LACUNA, Turton. 



Animal ; having a muzzle-shaped head, with two long tentacida, 

 bearing eyes or bulgings at the external bases. No neck-lobes ; 

 operculigerous lobe expanded or winged laterally, and furnished 

 behind ivith two filamentary processes, more or less developed, 

 but sometimes nearly obsolete. Foot rounded at both extremi- 

 ties, contracted at the sides, centrally grooved. Branchial plume 

 single. — Forbes. 



Shell; subglobosely or elongately turbinated ; spire sometimes very 

 short, sometimes prolonged, smooth, covered ivith an epidermis; 

 columella peculiarly grooved and umbilicated. Operculum 

 semicircular, horny, spiral. 



Under this head is comprised a small genus of mollusks, well repre- 

 sented on our own shores, where they live attached to seaweed. The spe- 

 cies are few in number, but extremely variable in form ; they are however 

 always characterized by the presence of a peculiar grooved umbilicus. In 

 Lacunce pallidula and puteolus the shell is of a globose, wide-mouthed 

 form, with a very small spire, whilst in L. crassior and vincta it is oblong 

 and turbinated. The peculiarities of the animal, first noted by Philippi, 

 have been more fully observed and described by the Swedish conchologist 

 Loveu, and by Edward Forbes. The above-named four species, having 

 various synonyms, inhabit the European coasts, and Dr. Gould describes 

 one as being peculiar to Massachusetts at Chelsea Beach. 



z a 



