106 CYCLADIDxE. 



beaks large, full, prominent, placed very much towards the anterior, 

 in which direction they are slightly inclined ; sulcations coarse, 

 moderately regular ; epidermis light green ; liga- 

 ment conspicuous ; valves solid, interior light blue ; 

 hinge-margin much curved, broad ; cardinal teeth 

 strong, representing the letter V reversed ; lateral 

 teeth elongated, strong. Length, nine sixteenlhs 

 of an inch ; breadth (height), six sixteenths of an 

 ve^ntnnum. i^ch ; l)rcadth, four sixteenths of an inch. 

 Euiarged. Inhabits Lakes Champlain and Memphraniagog, 



Vermont. Quite rare. 



Remarkal>le for its very oljlique and tumid shape, and for the 

 abruptness of its anterior margin. Compared with S. stamitieum 

 it is more tumid and less heavily sulcated ; it is less elongated and 

 more tumid than >S. striatinum. (Copied from Proc. Acad. Nat. 

 8c. xii. 408.) 



Sphserium truncatum. 



Shell thin and lucid, olivaceous, beaks elevated, hinder end truncated. 



Cyclas truncnta, Linsley, described by Gould in Sillim. Journ. new series, vi. 234, wood- 

 cut 3 (1848). — Prime, Proc. Bost. Soc. iv. 165. — Jay, Catal. 4th ed. 466. 



Cyclas cahjculata, C. B. Adams, Sdlim Journ. xl. 277 (1841); in Thompson's Nat. 

 Hist. Verm. 168 (1853) ; Land and Fresh- Water Shells of Vermont, 18. 



Cyclas pelbidda, Prime, in Stimpsox's Shells of New England, 16 (1851) ; Proc. Bost. 

 Soc. iv. 277 (1852). 



Sphcerium tnmcatum, Adams, Gen. ii. 451 (1858); Prime, Proc. Acad. Nat. So. xi. 301 

 (1860) ; Op. cit. xiii. 35 (1862). 



Sphcerium pdluculum, Adams, Gen. ii. 450 (1858). 



Shell rather large, thin, fragile, lucid, rather tumid, rounded-oval, 

 beaks a little anterior, elevated and tumid, posterior part highest 

 and abruptly rounded so as to appear somewhat trun- 

 cated ; anterior end regularly rounded ; ventral mar- 

 gin very little curved ; surface delicately and regularly 

 striated by the lines of growth ; epidermis pale horn- 

 s.truncatmn. color iiicliiiiiig to ollvc. Iiitcrior bluish. Hhige-mar- 

 E"i^"o'^-J- gjj^ delicate, cardinal teeth oljtuse, very minute, mar- 

 ginal teeth slender but well developed. Length, one third of an 

 inch ; height, one fourth of an inch ; breadth, one fifth of an inch. 

 Found in the New England States, New York, and Ohio. 

 It is nearly allied to »S. piirtumemm, but is less tumid, posteriorly 

 more elevated, and somewhat squarely clipped. It is very closely 

 allied to S. lacustre, Fer. (C caJyculata of most authors), and by 

 some has been regarded as identical with it. 



