GEMMA. 137 



latter with a small sinus. Length, four fifths of an inch ; heioht, 

 three fifths of an inch ; breadth, nine fortieths of an inch. 1 have 

 since seen a specimen one and one half by one and one eighth inches 

 in length and height. 



Of this shell I have three specimens, brought from the Bank fish- 

 eries. Tiie largest is proportionally more convex than the others, 

 and the ridges are less definite. Halifax and Fishing Banks ( WU- 

 lis); in the Copenhagen Museum, from Nahlsalik, Greenland {Beck). 



1 know of no species very closely ai)proaching this. Most of those 

 allied to it have the posterior extrenfity more or less angular ; this 

 is always accurately rounded. The ridges and grooves of the sur- 

 face are like those of F. paplllonacca. Venus ce.nca of Turton, small 

 specimens of V. g-al/uui, and of those Indian species allied to V. 

 papilionacca, may be mentioned as allied to it. 



Ocnuf^ GEl^IMA, Desiiayes. 1853. 

 Shell rounded, trigonal, beaks nearly central, three cardinal teeth 

 in the left valve, the median one conic triangular and a little curved, 

 in the right valve two diverging teeth with a wide interposed pit ; 

 pallial impression marginal, with a long, narrow, ascending sinus. 

 Animal with siphons connate, the lower one longer and fringed, 

 the upper one valvular ; foot semilunar. 



Gemma gemma. 



Fig. 51. 



Shell minute, nearly round and nearly equipartite, concentrically furrowed, 

 violet and white, margin crenulate. 



Venus (jem ma, Totten, Siliim. Journ. xxvi. 367, fin:s. 2, a-d (1834). — Gould, Inv. 88, 



fijT. 5L — SowLRi'.Y, Thes. Conch, ii. 737, pi. 158, fig. 141. — Wood, Ind. Suppl. pi. 



15, fig. 45. -De Kay, Nat. Hist. New York, 218, pi. 27, fig. 277. — Hanley, Dcscr. 



Cat. 126. — Stimpsok, Shells of New Eng. 19. — Reeve, Conch. Icon. pi. 25, fig. 128. 

 Gemma Totteui, Stimpsox, Check Lists (1860). 

 Gemma f/emma, Chenu, Man. dc Conch, ii. 83 (1862), fig. 359. —Adams, Gen. ii. 419, 



pL 107, figs. 3, 3«. — Deshayes, Cat. Brit. Mus. (Biv.) 113 (1853). 

 Cyrena purpurea, U. C. Lea, Sillini. .Journ. xlii. 106, pi. 1, fig. 1 (young). 



Shell small, nearly orljicular, beaks nearly central, slightly ele- 

 vated ; generally eroded. No defined lunule in front of them ; sur- 

 face shining, with minute, concentric, crowded furrows ; anterior 

 portion, and mostly the base, white or tinged with rose-color ; ])0S- 

 terior and upper portion reddish-purple ; within white, except poste- 



