168 



NATURAL HISTORY OF VERMONT. 



Part I, 



FRESH WATKR AND LAND SHELLS. 



FAMILY CONCHACEA. 



Genus Cvclas. 



Generic Guirnckrs.-S\w\\ small. iliin, globose- 

 elliplic, hinge will) lwi> minute cardinal leelh in 

 eacli or in one valve, whicli are someiitnes ohso- 

 lete, with coinpressed laleral leelli on oach side. 

 Animal whh ihe inanile posleriorly [iroloniicd into 

 two siphons, which have no retractor muscle ; fool 

 very tliiu and long. 



Cijclus d'gn lis . — A dams. 

 DESCRiPTioN.-Shell subglobular, rhom- 

 bic-orbicular, equilateral, finely and ele- 

 gantly striated ; epidermis rather light 

 olive green, with two straw-colored con- 

 centric zones, of which the exterior is 

 marginal ; beaks not prominent, slightly 

 nnduiate ; umbones very thin ; within 

 bluish ; lateral teeth large and strong ; 

 cardinal teeth rudimentary. Length OA'.i 

 inch ; height 0.36 inch ; width 0.:^6 inch. 



Remarks. — This species was discover- 

 ed in Weybridge, in a swamp, near the 

 site of an old i ndian encampment. It has 

 also been found at Burlington. It is re- 

 markable for its shining and elegantly 

 striated surface, and for its inflation, 

 which continues far over the disc, and 

 terminates abruptly near the margin. C. 

 rlwinbo'uhi, Sav, resembles it, but has 

 coarse strite, no yellow zones, and the 

 discs are less inflated. This is a rare spe- 

 cies, and the most beautiful of the genus 

 in our knowledge. 



Cyclus similis. — S \ v. 



Description. — Shell subelliptic, near- 

 ly equilateral ; epidermis dark brown or 

 yellowish and greenish brown; striw of 

 growth coarse, deep ; umbones not much 

 inflated, broad ; disc rather ttimid ; ante- 

 rior and posterior margins subrcctilincal 

 and divergent; inferior and superior mar- 

 gins rounded; within bluish; cardinal 

 teeth small ; lateral teeth compressed, 

 strong. Length 0.68 inch, height 0..5 inch, 

 width 0.4 inch. 



Rejfarks — Tiie form of the young dif- 

 fers much from that of the adult. It is 

 rectangular, longer than high, and much 

 compressed. Tiiis species differs from the 

 preceding in the coarseness of the strite ; 

 the discs near the margin are less tumid, 

 and the form is much less quadrilateral, 

 and the young, although quadrilateral, 

 are lonn-er and much more compressed. 

 Sometimes there are in tliis species also 

 yellow zones. 



Cydas rho/nloida. — Say. 



Description. — Shell rhombic, nearly 

 equilateral, very coarsely striate; epider- 

 mis yellowish horn color; beaks not pro- 

 minent, nor undulate ; umbones promi- 

 nent ; discs moderately tumid; anterior 

 and posterior margins nearly straight, di- 

 vergent; superior and inferior margins 

 moderately curved; within white; car- 

 dinal teeth rudimentary, lateral teeth 

 strong. Length 0.4G inch, height 0.38 

 inch, width 0.;27 inch. 



Remarks. — This species is very nearly 

 allied to the preceding, but the difference 

 is constant. That shell is longer, and the 

 umbones less elevated. The young of 

 this species, although rectangular, are 

 more tumid, which is the cause of the dif- 

 ference in the umbones of mature shells. 

 This s|)ecies is very plentiful in lake 

 Champlain, and is the only one which oc- 

 curs in the open waters of the lake in its 

 southern part. 



Ctjchis ■partumcia. — Say. 



Description. — Shell ovate-globose, 

 higher behind, nearly equilateral, very 

 thin, translucent, ratlier finely striate ; 

 epidermis shining, straw color, or bluish 

 horn color; beaks not prominent; um- 

 bones moderately tumid ; discs much in- 

 flated and quite regularly convex ; poste- 

 rior and hinge margins nearly straight ; 

 other margins much rounded ; cardinal 

 teeth small ; lateral teeth much develop- 

 ed, compressed. Length 0.3 inch, height 

 0.25 inch, width 0.17 inch. 



Remarks. — Tliis species inhabits stag- 

 nant water, and even swam|)s which are 

 dried during the autumn. The young are 

 less tumid, very regularly elli])tical, and 

 of a light honey yellow. In Massachu- 

 setts this species attains a greater size. It 

 resembles C. cnrnea of Euro]>e, which, 

 however, is wider, has the umbones more 

 prominent, and both sides of equal height. 

 C. similis is longer, much larger, and more 

 coarsely striate. 



Cijclus cdlyculata. — Drap. 



Description. — Shell rhombic orbicu- 

 lar, higher behind, nearly eqtiilateral, ex- 

 tremely thin and fragile, translucent, witli 

 very fine striffi ; epidermis shining, bluish 

 horn color, or lemon yellow ; beaks swol- 

 len, and very prominent, resembling knobs; 

 umbones moderately tumid ; discs witii a 

 small degree of convexity ; posterior and 

 hinge margins nearly straight, making tin 

 obtuse angle ; anterior and inferior mar- 

 gins rounded ; anterior much shorter than 

 the posterior margin ; cardinal teeth ex- 

 tremely minute; lateral teeth small, com- 

 pressed ; inner surface colored like the 



