1 4< I ISCHNOCHITON-RADSIELL A . 



chiton*, hut insertion-plates of the intermediate valves having twoor 

 several slits. 



The present section differs from Ischnoradaia Shuttleworth (Lep- 

 idora<l*in ( 'pr.j, in having the girdle covered with flat, striated scales, 

 whilst in the latter group the scales are transformed into smooth, 

 solid, pebble-like bodies. Radsiella differs from the Radsioid section 

 /v/f/xw in having the short contour and anterior mucro of the 

 true Ischnoehitons, and in the normal foot and gills. 



Carpenter's use of the name Ischnoradsia Shutthv. for this group 

 is clearly indefensible, as Shuttleworth mentions none of the 

 > now included herein, whilst his diagnosis covers all Radsioid 

 forms of Iscknochiton. I have therefore restricted the namelschno- 

 r>i'l*ia to the forms grouping around Shuttleworth's first species, 

 auttralis. 



I. TKIDKNTATUS Pilsbry, n. sp. PL 18, figs. 35, 36, 37, 38, 39. 



Shell small, oval, moderately arched, slate-color with white spots 

 and dots, or white mottled with slate ; the girdle tessellated with 

 alternate dark and light, the interior blue, with a leaden spot under 

 each BUtural-plate, and short dark rays from the apex. 



The valves are evenly arched. The posterior valve (fig. 39) has 

 a central, rather depressed umbo, the slope behind it concave. 

 Lateral areas raised a trifle, but scarcely distinguishable; central 

 areas evenly, closely and finely pitted in quincuncial pattern ; the 

 lateral areas are a little more coarsely sculptured with close low 

 diamond-shaped granules ; the granulation generally less regularly 

 arranged on the end valves than on the lateral areas. 



Interior with low, arched sutural-plates and wide, flat, angular 

 sinus; anterior valve with 13, posterior 12, central valves 2 slits. 

 Teeth sharp, smooth. Eaves very narrow. 



Girdle covered with imbricating striated scales (fig. 36.) 



Length 15, breadth 10 mill. 



l.aTnz, Lower California (Lockington) ; Gulf of California 

 (Gab!..; 



/ M ,/'/</, -l,t d ispar C A i : i i : N r i : K, ^fS. n ot Sow i : i : i : v . 

 This species is easily separated from I. dispar Sowh. by the 

 apparently similar sculpture of central and lateral arras, the sculpt- 

 ure in iH*intr being obviously diverse on these areas. I suppose this 

 to be what Carpenter considered ih'.tpar merely because it has 

 valves : but Carpenter has given no description of his shells. 



