ISCHNOCHITON-RADSIELLA. 141. 



The foot is not produced forward beneath the head, as it is in 

 Stenoradsia. The gills extend from the front end of the foot to 

 within somewhat less than the width of a valve from the tail end. 



I. VIRIDULUS Couthouy. PI? 17, figs. 32, 33. 



Shell small, oblong, rather elevated and decidedly carinated ; 

 creamy yellow, or " of a very pale olive or drab color." Surface 

 smooth to the naked eye, but under a lens it is seen to be every- 

 where covered with low granules quincuncially arranged. The 

 lateral areas are a trifle raised, but not distinctly so, and upon them 

 the granulation is somewhat effaced, and a few very obsolete radiat- 

 ing sulci are generally distinguishable, as well as several rather 

 strongly indicated growth-periods. " Interior: posterior valve hav- 

 ing 13-14, (rarely 17), anterior valve 14-16, central valves 2-3 

 slits. Teeth acute, distant ; eaves acute, projecting, hardly spongy ; 

 sinus wide, short, flat. Girdle covered with rather large, wide 

 scales, deeply and distantly striated." Length 13, breadth 7 mill. 



Orange Harbor, Terra del Fuego. 



Ch. viridulus COUTH. MS., GOULD, Proc. Bost. Soc. N. H. ii, p. 

 144, 1846; Otia Conch., p. 5 ; U. S. Expl. Exped., Moll., p. 318; 

 atlas, f. 413. Ischnoradsia viridulas CPR., MS. Lepidopleurus viri- 

 dulus ROCHEBR., Miss. Cape Horn, Polyplacophores, p. 140. 

 ? Ischnochiton viridulus Gld., HADDON, Challenger Rep., p. 16,1886. 



A small form, evenly granulated, and having indistinct lateral 

 areas. I have taken the description of the internal parts from 

 Carpenter's MS., as I have not examined the interior of the single 

 specimen before me, which is one of the original lot. 



I. TRIFIDUS Carpenter. PI. 18, fig. 40. 



Shell rather large, rather elevated, regularly oval ; red-chestnut, 

 maculated with lighter and darker; jugum acute, gothic. Mucro 

 median, flat ; entire surface very minutely granulated ; central areas 

 having about 8 strongly punctate lines perpendicular to the jugum ; 

 lateral areas strongly defined, having 2 to 4 obsolete ribs, sometimes 

 punctate in the interstices. 



Interior whitish flesh-colored, with two reddish-purple rays diverg- 

 ing from the flat umbones ; posterior valve having 13, anterior 13, 

 central valves 2 slits ; teeth acute, sometimes serrated at the edge, 

 sometimes striated outside, sometimes smooth. Eaves subspongy ; 

 sinus small, laminate, the lamina slit at the sides and sometimes in 



