GEMJIA. 137 



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

 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. Tlie largest is i)roportionally more convex than the others, 

 and the ridges are less dehnite. Halifax and Fishing Banks ( Wil- 

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



I know of no species very closely approaching this. Most of those 

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

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

 face are like those of V. papilionacea. Venus wnea of Turton, small 

 specimens of V. g-allimi, and of those Indian species allied to V. 

 papilionacea, may be mentioned as allied to it. 



Oentis GEITIITIA, Deshayes. 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 gemma, Tottex, Sillim. Joiini. xxvi. 367, figs. 2, a-d (1834). — Gould, Inv. 88, 



fig. 51. — SowERBY, Thcs. 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, Descr. 



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

 Gemma Totfeni, Stimpson, Check Lists (1860). 

 Gemma (jemma, Chenu, Man. do Conch, ii. 83 (1862), fig. 359. — Adams, Gen. ii. 419, 



pi. 107, figs. 3, 3 a. — Deshayes, Cat. Brit. Mus. (Biv.) 113 (1853). 

 Cyrena purpurea, H. C. Lea, Sillim. Journ. xlii. 106, pi. 1, fig. 1 (young). 



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

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

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

 portion, and mostly the base, white or tinged with rose-color ; pos- 

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



