ISCHN'H IMTON. 



tionnl xrnVx of jinKfnlrs whirh drntntc the sutures. Central areas hav- 

 ing about Hi iicnfr, narrow, elevated longitudinal ///>*, becoming 

 divergent at. the outer an^le; those :it tin- dorsal ridi:e -mailer and 

 moiv crennlated ; the deep and wide interstices bring finely, irregu- 

 larly wrinkled arro.-s. Anterior border of tegmen turn e !<-<j<t nfty seal- 

 lojiftf. Anterior valve having about 13 (or more) low rounded ribs, 

 bearing brown ])iistules, like the lateral areas; many of the ribs 

 splitting into t\\<> or more toward the peripheral margin, the rows 

 of pustules doubling to correspond. Posterior valve having the mucro 

 Jlut, and 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 t 

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

 laminse 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. BISCLTLPTUS 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 shalloiv sulcus down the 

 middle, and bearing three (on valve ii, four) irregular radialseries 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 about 10 narrow, 

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

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

 minutely granulated. Anterior valve minutely granulated, and 



