376 PBOCEEDINGS OF THE NATIONAL MUSEUM. 



otherwise marked occasioiuilly with faint interrupted linear rajs. A 

 rare form. The two-rayed cxauii)le.s in this Grou]),as well as in Group 

 II, are quite rare. 



Variety ;', triserialis. 



Three white or light-colored rays; the middle one fienerally the most 

 conspicuous, sometimes extending nearly to the ventral edges, often 

 (juite broad and formed by the coalescing of numerous narrow linear 

 rays; the surlace of the valves often exhibit faint lineation or sugges- 

 tions of rays, also stipidc-like markings, l^.xtreme ti])s of umbos gen- 

 erally purple, though sometimes light. 



Frequently the rays on both of the foregoing varieties are only 

 slightly exhibited at the beaks. 



Variety c, aurora. 



Tmbonal region wdiitish; this tint covers about one-third of the sur- 

 face of the valves from the beaks, the edge of this whitish area closely 

 linearly rayed, suggesting the llame likeradiati(ms from the upper edge 

 of the "northern lights;" the rest of the surface of the valves pale, 

 dingy purplish brown, with zones of pale purple and pale brown. This 

 is a variety of very rare occurrence. 



GROUP VI. 



This grou)) includes individuals which exhibit two series of rays, 

 dark and light, in the same shell. 



Variety o, duplicata. 



This is a very rare and pretty variety, in which the general tone of 

 the ground is pale purplish brown, with somewhat darker /.ones. It 

 differs from all of the other layed varieties in this, that it has the dark 

 rays of Grouj) 1 and the light rays of (inmp V. The light rays are 

 short in some instau(;es; in others the middle light ray extends nearly 

 to the ventral margin, i ha\e found only seven examples in a thou- 

 sand specimens. The dark rays vary in number; in one example these 

 are as numerous as in N'ariety fi, mnUiradiaia. 



In most of the loregoing there are sub varietal aspects readily per- 

 ceived by the eye, but not so pronounced as to admit of a description 

 that would enable one to determine them without a colored figure. 



The color variation herein described is exceedingly local, the varieties 

 mentioned under Group I excepted. Of these, miiltlrmUata is appar- 

 ently restricted to the Santa Monica region, as well as lutcohrnmiea, 



Mr. Hemphill informed me that the only color variety occurring at 

 San Diego and the region thereabout is ochracea, of Group III. 



