- 581 - 



marf in anf? '''^r'-' -^'o^tral "lar .. ^ abparallel th r ■^ -■•'-■'■-,' ■-^■-■'t ..^x 

 lengtTi, the ventra.l margin vev^ f ee^bly insinuated ;riecTially "by 

 a slight compression of the sl^ell near the marn-in; abrixptly 

 roiUided posteriorlj-, more eonvezli" roiiiidel anteriorl;^; ^•"•^'bones 

 low, plaee^^ near the posterior end; external siirface 'vith fine, 

 inconspionous inorementals; the "cardinal" of the left valve 

 place utTore the urnbo, curved parallel to the mar ' ; ;he lat- 

 eral laminae strong, the posterior long; chonriropl. c . 



Dimension s.- Length, S.5 nra. ; a" ' . , 1.8 mm.; semidiara. , 

 .8 mm. 



Remarks .- This species, the tj^pe of Gahh's genus Feaero- 

 m:;a , is, as "Hall (1) has pointed oixt, a typical "'rj^ci c . .."'_; 



fl). Trans. Wagner ITree Inst, Sci . , PhiladeVohia, vol* r-5, -ot . 

 5, p. 1145, 1900. 



collections at hand have furnished two small left valves, snBller 

 than the t;,"pe. I'hei^ are recognized hj' their luiu.. L^aiij elongated 

 outline and virtually parallel dorsal snd ventral margins. Hall 

 (2) has already noted the occiu-rence of this form in the Borden 



i2). Idem. 



faixna. 



