HELCIONISCUS. 131 



(3). JAPANESE AND CHINESE SPECIES. 



The Patellas of this region may be distinguished by the key 

 given below. 



Neither P. clypeater nor P. argentata (cuprea) inhabit Japan, the 

 citations of these species by Schrenck and Dunker being erroneous. 



Key to Japanese Patellidce. 



Shell more or less silvery or iridescent inside (ffelcioniscus.) 



Conical, having about 50 strong, close elevated riblets, alternating 



[or subequal in size. 

 Large, light buff; border of the inside narrow, yellowish, 



H. Boninensis Pils. 



Variegated with brown ; border of the inside conspicuously 



black-blotched, H. Stearnsii Pils. 



Conical, having several smaller riblets in each interval between 



the larger ribs, H. pallidus Gld. 



Ribs fine or obsolete. 



Solid, with radiating dark lines ; spatula orange-red ; ribs 

 obsolete, H. nigrolineatus Rve. 



Thin, with very finely beaded riblets or stria?, 



H. amussitatus Rve. 



Thin, with very fine strise, not beaded, H. toreuma Rve. 



Shell porcellanous inside, opaque, not iridescent (Scntellastra.') 



Depressed, having strong irregular ribs, P. stellceformis Rve. 



H. BOXINENSIS Pilsbry. PI. 66, figs. 1,2; pi. 67, fig. 3. 



Shell large, solid, oval, erectly, straightly conical, the apex a little 

 in front of the middle ; posterior slope a little convex, the other 

 slopes straight; basal side-margins a little elevated, so that the 

 shell is supported by the ends alone when resting upon a plane sur- 

 face. 



Sculptured with numerous (48-55) subequal radiating ribs (and 

 sometimes some small interstitial riblets), the ribs varying from 

 closely and rather weakly crenulated to strongly tubercled. 



The color is a uniform light buff, somewhat soiled, and having 

 sometimes a few small black spots around the apex. 



Interior: the muscle-impression is of a snowy or bluish-white; 

 outside of it there is a broad band varying in different individuals 

 from creamy-brown to deep chestnut, outside of which there is a 

 silvery, slightly iridescent zone, extending to the narrow yellow 



