HELCIONISCUS. 127 



number; a few small intervening riblets often developed. Color 

 typically almost black. 



Interior somewhat silvery, leaden-bluish, showing the dark ribs ; 

 central area black, whitish in front, sometimes entirely white ; often 

 of a beautiful purple. 



Length 40, breadth 34, alt. 16 mill. 



Sandwich Islands. 



Patella exarata NUTT., Jay's Catal., p. 38 ; REEVE, Conch. Icon., 

 f. 47a, 47b, and 62a, 62b, 1854. PEASE, Amer. Journ. Conch, vii, 

 p. 198, 1872. P. sandwichensis PEASE, P. Z. S. 1860, p. 537; 

 Amer. Journ. Conch, vii, p. 198, 1872.---P. undato-lirata REEVE, 

 Conch. Icon., f. 59. Helcionizcus exaratus DALL,, Amer. Journ. 

 Conch, vi, p. 279, t. 16, f. 29 (dentition). Patella lugubris Blainv., 

 DESK. Trait. Ele"m. de Conchyl., Atlas, t. 62, f. 13, 14. (non Blain.) 



This common Patella of the Sandwich Is. is readily known by its 

 numerous strong black ribs. It is so variable, and intermediate 

 forms are so numerous, that varietal names are scarcely admissible. 



Some individuals (figs. 6, 7) are drab or gray, closely spotted with 

 black on the upper part of the cone, and having the ribs nodulose, 

 as in Patella nigrisquamata. 



This species has been reported by Schrenck from the bay ot 

 Hakodadi, Japan. His specimens were identified by a comparison 

 with Reeve's figures, not by comparison with actual specimens. In 

 all probability the Japanese specimens were imported, as were those 

 said by Reeve to be from Oregon. 



The typical exarata, as first defined and figured by Reeve, is dark, 

 with black ribs (figs. 8, 9, 10.) 



Pease states that his sandwichensis differs from typical exarata in 

 being thicker, more elevated, ribs generally larger, wider apart, more 

 prominent, and crenate or scabrous, generally having smaller inter- 

 mediate riblets. It is generally white inside. It inhabits deeper 

 water, and according to Mr. Pease, differs in taste from typical 

 exarata ! 



The form called lutrata Nutt. (pi. 47, figs. 1, 2, 3) is white, with a 

 few of the ribs brown. The central callus of the interior is white. 



H. ARGENTATUS Sowerby. PI. 18, figs. 29, 30 ; pi. 65, fig. 93. 



Shell large, solid, of a dome-like conical form, oval ; slopes con- 

 vex ; apex subcentral (in the young more or less anterior). Sculp- 

 tured with very numerous unequal radiating riblets. Color chest- 



