PATELLA. 91 



37) strong radiating ribs, most of which are compound, as if formed 

 by the coalescence of several smaller ribs. Color dull black, some- 

 times rayed with white. 



Interior blue, the central area either blue or white ; border crenu- 

 lated. Length 60, breadth 50 alt. 20 mill. 



Loanda and Benguela, Guinea ; Cape Verde Is. 



P. lugubris GMELIN, Syst. p. 3705. REEVE, Conch. Icon. f. 32, 

 1854. DUNKER, Ind. Moll. Gum. Infer, p. 38, t. 7, f. 9-11, 22-24. 



The uniform black color is sometimes relieved by light rays, visi- 

 ble inside, and sometimes the whole central area is white, the black 

 rays not extending to the apex. These color-marks are best seen 

 by looking through the shell at a strong light. The ribs are usually 

 seen to be compound, or partially split into several smaller riblets ; 

 but of the principal ribs there are generally about 34. 



P. PLUMBEA Lamarck. PL 24, figs. 11, 14, 15 ; pi. 57, figs. 38, 39. 



Shell low-conic, oval or elliptical, rather solid; apex at the ante- 

 rior two-fifths of the shell's length ; slopes convex. Surface 

 sculptured with numerous riblets, sometimes narrow, irregular and 

 close, sometimes separated. Color dull black, sometimes rayed 

 with grayish, the rays scarcely perceptible outside. 



Interior blue, the central area elongated, white, often clouded or 

 stained with rich brown. Margin crenulated. 



Length 53, breadth 42, alt, 15 mill. 



Senegal ; St. Helena. 



P.plumbea LAM., An. s. Vert.vi, p. 328, 1819. DESH., /. c.vii,p. 

 530. REEVE, Conch. Icon. f. 5 and 46. E. A. SMITH, P. Z. S. 

 1890, p. 296. P. ccerulea QUOY & GAIM., Voy. de F Astro!. Moll., 

 iii, p. 342, t, 70, f. 4-6. P. cyanea LESSON, Voy. de la Coquille, ii, 

 p. 417. P. canescens RVE., Conch. Icon. f. 103. 



This species is extremely variable in sculpture. The ribs are 

 narrow, rather separated, but often increased in number and close- 

 ness by the secondary ribbing which transforms each rib into three, 

 the middle one larger. The ribbing is finer than in P. lugubris, the 

 shell is more elliptical, more depressed, and the central spatula of 

 the interior is longer and narrower. 



The variations exhibited by the series before me cause me to 

 regard P. safiana Lam. and compicua Phil, as close allies, possibly 

 varieties of this species. 



