TONICELLA. 45 



Trachydermon were it not for the peculiar blunt teeth, ambient 

 gills and almost scaleless girdle. ^ 



The girdle seems to be dusted with a few small, smooth white 

 scales in places. 



On account of the spongy eaves and hairless girdle, I include 

 this subgenus in Tonicella rather than in Chcetopleura ; but its 

 close affinities with both of these groups renders the question of 

 its position peculiarly difficult. 



T. HARTWEGII Carpenter. PL 14, figs. 81. 82, 83, 84, 85. 



Shell oval, rather low, the dorsal ridge obtusely rounded ; dull 

 olive green, generally having a pair of lighter stripes on the ridge 

 of each valve with a black blotch outside of the light dashes. 

 Girdle (fig. 82) rather narrow, dense, microscopically closely 

 granulated. 



The tail valve is convex as a whole, but the subcentral umbo is 

 not conspicuous. The entire surface is very closely microscopically 

 granulated, and bears larger wart- Like granules irregularly scattered 

 over the minute sculpture, these warts being much more numerous 

 upon the lateral areas (which are otherwise rather ill-defined) and 

 the terminal valves. 



The interior is of an intense blue-green color. Sutural plates 

 rounded, leaving a wide, angular sinus. Insertion plates shorter 

 than the eaves, blunt, the anterior valve having the teeth bi- or tri- 

 lobed, the posterior valve having them crenulated. Slits of ante- 

 rior valve 10-11 ; median valves 1 ; posterior valves 9-12. Eaves 

 spongy. 



Gills extending forward to the front end of the foot. 



Length 30, breadth 17 mill. 



Length 27, breadth 18 mill. 



Vancouver Island to Magdalena Bay, Lower California. 



Chiton hartwegii CPR. P. Z. S. 1855, p. 231 ; Trachydermon hart- 

 wegii CPR. B. A. Rep. 1863, p. 649. Chcetopleura hartwegii CPR. 

 MS. p. 45. DALL, Proc. U. S. Nat. Mus. 1878, p. 329. 



The prominent differential characters of this species are its sys- 

 tem of sculpture, vivid blue-green interior, slightly spongy eaves, 

 stumpy, bilobed teeth of the front valve, etc. 



