86 ISCHNOCHITON. 



Posterior valve having 14, central 1, anterior 12 slits; typically 

 Ischnoid ; teeth sharp, very thin ; sinus appears smooth, rather 



Length 8J, breadth 4f mill. ; divergence 108. 



Carpenter does not state whether the interior described is that of 

 the " Lepidopleurus" or the Ischnockiton which are included under 

 this species. Probably both are young, and the types evidently 

 require further study. The name luzonicus should be restricted to 

 the form with convex, smooth scales, and the systematic position of 

 it is probably in the section Lepidozona of Ischnochiton. 



Section Ischnoradsia Shuttlew. 



I. TRIFIDUS Cpr. PI. 17, figs. 64, 65, 66, 67. 



See Vol. XIV, p. 141, for the original description. 



The shell is elevated and carinated, side-slopes slightly convex. 

 Color reddish-brown, maculated with buff and purple-brown, the 

 dark color generally predominating. 



Valves squared, not beaked. Lateral areas slightly elevated, cut 

 into three low, flat ribs by two radial narrow grooves, which are gener- 

 ally somewhat pitted. Central areas having a number of rather 

 strong wrinkles or grooves, in the direction of growth-lines, these 

 grooves being conspicuously pitted or punctured, and closer toward 

 the anterior margin of each valve. Immediately in front of the 

 diagonal slope, especially toward the beaks, the pitting is finer and 

 closer. Anterior valve having about 18-23 broad, low ribs, separ- 

 ated by linear, punctured interstices. Posterior valve having the 

 mucro central, bent downward, but little projecting. 



Interior white, with purplish-red rays posteriorly. Anterior valve 

 having 13, median valves 2-2, posterior valve 13 slits, teeth dis- 

 tinctly roughened, almost pectinated outside. Across the sinus there 

 is a narrow lamina, notched where it joins the sutural-lamina3. 



Girdle compactly covered with solid, rather convex scales, which 

 are about '3 to '33 of a mill, in width (fig. 66). 



Length 27, breadth 17 mill.; divergence 100-110. 



Sitka to Victoria, British Columbia, 9-18 fms. 



This species is more correctly referred to Ischnoradsia than to 

 Radsiella, the scales being smooth and rather convex. It has no 

 near allies, the pattern of sculpture being extremely peculiar and 

 distinct from all other chitons which I have seen. The closeness of 



