719 - 



weak; on the left valve the posterior lateral or both posterior 

 and anterior sometimes absent; ri??ht laterals usfially present, 

 but sometimes wefsk; inner nBr.^ln of the va]ve finely crentilated. 



Dimensions .- Lat., 14.2 mm.; a3.t., 12.5 mm.; semidiamx., 

 3.8 nffii. 



Remark s . - The concentric sculpture as preserved is irregul- 

 '■■vli; developed since most of the valves are v/orn; there are present 

 however, irregularly spaced concentric lines of varying width 

 and sharpness, usually absent on the median dorscl rep-ion, as v.-ell 

 as incremental lines. xhe fine radials are usually preseiit over 

 the entire disk, ezcept in the umbonal region; they too are of 

 varying v^idth and -^Tom.inence. Bo:".: . ''S of scul-^oture are usually 

 conspicuous enough to produce a reticulated effec'-. Some varia- 

 tion is noticeable v/ith regard to aonvesity, but in general the 

 craracters are quite constant. 



This is an abundant form and various gro7rfch stages are repre- 

 sent e'', the valve measured being one of the largest . The small 

 size, slig"-tly elongate outline and fine rariial sculpture are 

 characteristic features. Dall noted the fact that Guppy's name 

 was pre-ocGupied, but hesitated to propose a st^ecific name since 

 he doubted whether the "r^~ro^ oouJJ-d "'-'-• ^'^^ -^if ically differentiated 

 from pertenera . The present form is, however, mxioh more abundant 

 than pertenera and presents constant 'Tifferenoes in being decid- 

 e-^ly small, more inflated, less ..1 .^ated, with more cons^:'icuous 



