ISCHNOCHITON. 83 



tlonal series of pustules which dentate the sutures. Central areas hav- 

 ing about 16 acute, narrow, elevated longitudinal ribs, becoming 

 divergent at the outer angle; those at the dorsal ridge smaller and 

 more crenulated ; the deep and wide interstices being finely, irregu- 

 larly wrinkled across. Anterior border of tegmentum elegantly scal- 

 loped. Anterior valve having about 18 (or more) low rounded ribs, 

 bearing brown pustules, like the lateral areas ; many of the ribs 

 splitting into two or more toward the peripheral margin, the rows 

 of pustules doubling to correspond. Posterior valve having the mucro 

 flat, mid a trifle in front of the middle; the posterior profile of the 

 valve sloping regularly down from the front margin (fig. 59.) 



Interior white, with a wide dark green ray on each side behind, 

 and a green patch on each side in front of the valve-callns. Anterior 

 valve having 8, median 1-1, posterior 9 slits; teeth acute, but finely 

 roughened inside and out toward the edge. Sinus straight, not 

 denticulate, having a narrow lamina separated from the sutural- 

 laniinse by a notch on each side (fig. 58.) 



Girdle covered with convex, weakly striated scales, averaging '37 

 mill, in width (fig. 57). 



Length about 17, breadth about 12 mill. ; divergence 108°. 



Hakodadi, Japan. 



The specimen figured is one of the original lot, no. 24144 of the 

 Smiths. Inst. Mus. The comparisons given on p. 132, of vol. xiv, 

 readily distinguish this from the allied forms. 



The riblets of the second valve diverge at the ridge. 



I. BiscuLPTUS Cpr. PI. 17, figs. 60, 61. 



The original description is given on p. 119, vol. xiv. 



The shell is thin, small, elevated, acutely carinated, the side-slopes 

 nearly straight. Pale green or yellow, maculated with dull green. 



Intermediate valves (fig. 61) squared, not beaked. Lateral areas 

 raised, very minutely granulated, showing a shallow sulcus doivnthe 

 middle, and bearing three (on valve ii, four) irregular radial series of 

 sparsely placed pustules ; the posterior ones few, and somewhat 

 dentating the sutures ; the median series often reduced to very few 

 pustules. Central areas having on each side aboid 10 narrow, 

 elevated longitudinal lirce, their interstices wide and finely, densely, 

 latticed across ; the ridge of each valve free or nearly free of ribs, 

 minutely granulated. Anterior valve minutely granulated, and 



