106 



cycladidj:. 



Fig. 410. 



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 sixteenths 

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

 inch ; breadth, four sixteenths of an inch. 



Inhabits Lakes Champlain and Memphramagog, 

 Vermont. Quite rare. 



Remarkable for its very oblique and tumid shape, and for the 

 abruptness of its anterior margin. Compared with S. stamineum 

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

 more tumid than S. strlatiaum. (Copied from Proc. Acad. Nat. 

 Sc. xii. 408.) 



S. Vennontanum. 

 Enlarged. 



Sphserium truncatum. 



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



Cydas truncnta, Linsley, described by Gould in Sillim. Jourii. now scries, vi. 234, wood- 

 cut .3 (1848). — Prime, Proc. Bost. Soc. iv. 1(55. — Jay, Catal. 4tli cd. 4G6. 



Cyclus caljjculata, C. B. Adams, Sillim Journ. xl. 277 (1841); in Thompson's Nat. 

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



Cydas peUucida, Prime, in Stimpson's Shells of New England, IG (18.51) ; Proc. Bost. 

 Soc. iv. 277 (18.52). 



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

 (1860) ; Op. cit. xiii. 35 (I8G2). 



Sphcerium jHlluciilum, 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 ai)i)car somewhat trun- 

 cated ; anterior end regularly rounded ; ventral mar- 

 gin very little curved ; surface delicately and regularly 

 striated by the lines of growth ; epidermis jxile horn- 

 color inclining to olive. Literior bluish. Hinge-mar- 

 gin delicate, cardinal teeth obtuse, very minute, mar- 

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

 inch ; height, one fourth of an inch ; l)readth, one fifth of an inch. 

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

 It is nearly allied to >S. partumeiuin, but is less tumid, posteriorly 

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

 allied to S. lacvstre, Fer. ((7. calyciilata of most authors), and by 

 some has been regarded as identical with it. 



Fig. 411. 



S. trinirntiim 

 Enlarged. 



