228 



having two well-defined slits on one side, suggesting the possibility of specimens 

 being, found with two slits, which is usual in this genus. I note a Japanese 

 species, /. albrechti, Schrenck, varies from one to three. 



Ischnochiton (Haploplax) misimaensis, n. sp. 



General appearance. — Elliptical, almost evenly arched, not carinated, shallow 

 radial ribs in lateral areas and end valves ; girdle clothed with polished, pebble- 

 like scales, all of which are dark on the lower or outer side, but those in the light 

 bands are transparent on the upperside. 



Colour. — The ground colour of the upperside is Tea-Green, thickly covered 

 with streaks and broad dashes of Mikado-Brown (Ridgway's Colour Standards, 

 pis. xlvii. and xxix. ). 



Inside. — Greyish-green, very similar to the upperside, anterior valve with 

 13 slits in the insertion plate, irregularly placed, posterior 15 slits, sutural laminae 

 shallow, anterior edge parallel with the tegmentum, sinus broad ; median valves 

 have 1-1 slit, sutural laminae somewhat rounded and rather large in proportion, 

 sinus between very broad, insertion plate teeth sharp and the slits deep. 



Anterior valve. — Raised, slope convex, shallow ribbing being distinguishable 

 towards the margin, which is slightly crenate, the whole surface is decussated 

 with minute, evenly-spaced granules. In the larger specimen it can be clearly 

 seen that these granules are arranged in narrow, radial rows, about three of 

 these forming the wider, flat, radial ribs, of which there are over 50 in each 

 end valve. 



Posterior valve. — Mucro a little anterior of middle, but little raised ; the 

 anterior portion occupies barely one-third of the valve, and the posterior two- 

 thirds is defined by being raised slightly, thereby forming a diagonal ridge ; the 

 sculpture of the anterior portion is similar to the pleural areas of the median 

 valves ; the posterior two-thirds is similarly sculptured, but has, in addition, 

 towards the outer margin, a suggestion of radial ribbing, but this in the type 

 is so shallow as to be hardly discernible ; several shallow-growth sulci are also 

 present. 



Median valves. — Evenly arched, not carinated, the dorsal area not defined, 

 the combined dorsal and pleural areas are decussate with evenly-distributed, 

 minute granules ; several growth sulci are continued from the lateral areas, 

 across the pleural area. The lateral areas are raised and well defined, covered 

 with granules similar to the rest of the shell, but, in addition, crossed by two 

 deep growth sulci and several minor ones ; incipient, broad, radial sulci can be 

 seen if the valve is held at a right angle. The large but crushed specimen in situ 

 on a black stone measuring 15^X11 mm. has five or six well-defined, flat, radial 

 ribs in this area, where they are two or three times as broad as is the case in the 

 end valves ; they are noticeable, even without the aid of a pocket lens. 



Girdle. — The girdle is broad banded, clothed with rather large, imbricating, 

 polished scales, which are blackish in the dark bands and opalescent above and 

 black below, on the outer side, in the lighter ones ; this rather unusual feature 

 is common to all the six specimens in the collection. The scales are polished, 

 and under 65 mag. those nearest the shell are distinctly striate ; the larger scales 

 in the centre of the girdle are, under this power, partially striate, the surface of 

 the scales is slightly rough, a subgranulose character that is not visible under a 

 pocket lens. In H. lentiginosus the surface of the scales is smooth, although 

 those immediately next the shell show some striae. 



In H. lentiginosus the upper margin of the scales is evenly rounded, whereas 

 in the species under review it is subtriangular. In the large damaged specimen 

 before referred to there is a well-defined, short, girdle fringe; in H. lentiginosus 

 in one or two specimens I can detect a less-developed fringe. 



