GEMMA. 137 



latter with a small sinus. L(>ngtli, foiu- 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 ])y one and one eighth inches 

 in length and heidit. 



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

 eries. The largest is })ro])ortionally more convex than the others, 

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

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



I know of no species very closely a^jproaching 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. papilioiiacea. Venus cenea of Turton, small 

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

 papilionacea, may be mentioned as allied to it. 



Oeiiiis GE.li:?IA, Dksiiayes. 18r,3. 



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, mars^in crenulate. 



o 



Venus gemma, Tottex, Sillim. Journ. xxvi. 367, fijis. 2, a-d (1834). — Gould, Inv. 88, 



fig. 51. — SowEKBT, Thes. Conch, ii. 737, pi. 158, fig. 141. — Wood, Iiid. Suppl. pi. 



15, fig. 45. -De Kay, Xat. Hist. New York, 218, pi. 27, fig. 277. — PLvnley, Descr. 



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

 Gemma Totteni, Stimpson, Check Lists (1860). 

 Gemma gemma, Cheno, Man. de Conch, ii. 83 (1862), fig. 359. — Adams, Gen. ii. 419, 



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

 Ci/rena 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. Xo 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 ; wnthin white, except poste- 



