Ll l'\ 

 ill*. I 



-lightly uli]i(|in>. deepest in iN loner ji.irt. nai rou HIL' aho\e l>\ tin >|nnont of a 



low swelling on each side, tliiit <ui tin- .intern n M< le more prominent than t he -.( hei : 

 ;i not very prominent, rounded tuliercle near tin- lower part nf tin- anterior l.onlcr; 

 excepting tin- siilcu- ami the llattened l.onler. the entne Mirf.ice i- beautifully 



;ilated. 



This lin > i- proliaMy more c|o-ely related to /'. nTilleri I'lnch. from the 



upper I.eds of the ('inciiiiiati ^roup. tlian to any other known. The si/.e of /'. millrri 

 U somewhat jjreab'r. its length liein^ usually a little more than l.d mm. Hut tin- 

 real ilinVrei. A'een the two form- an- (1) the prnport ioually greater length of 



the \al\e- aii'l of the liin^e in the Minnesota -|.eei. t* longer ami otherwise 



ilillerent ->ulcu>. ami i -esiou of a romi'leu. anter- ly situated 



tulierele. whieh i- wanting in the <IH. e;j. 



n .in./ I.M-.ility i'|,|-r tlnnl nl &, SU Paul anil m>ar Canrmn I 



MlnnoHoUu 



I'KIMITIA MKI p. 



.;s. m-n. 



l.'-iikMli ii '!' inn, ' i'. nun .: Ihii-kneMa 0.23 nun. 



Thi- Aperies, though inui-h smaller, seems to be relate.! to /' /muti. It i- 



however relatively shorter, with a longer hinye line and stronger dorsal angles. The 

 valve is strongly convex, especially in the posterior half, ami the prominences on 

 each -i'le of the curved suleus are leeidedly higher than in the larger spe' 



n. that >j.eeies lias a rounded tulierele in front which is wanting in /'. mirtt/n. 

 Filially, the surface i- only olcurely punctate and not reticulate. 



It is perhaps more d. I to /'. /itni!<lnla of the Hudson Kiver shales, 



luit. aside from it> much smaller -i/e. it is at once distinguished hy the absence of 

 the narrow curve.! rid^e. running a short di-tance within the ventral margin in that 



ilooa shales near ( \IinnefloU; aoclatd with /'. uphami, 



llythoryfirii rylin<ti 



I'lMMI 



s <r. and at. 

 L. iiK-th n '.7 nun . In. Uii.-kness 0.30 nun. 



Valve> with the hack |i . the dor-al angles di.-tinct 



though not sharp, the onds ahoiit e.|ually curved though the anterior i> somewhat 

 narrower than the posterior: ventral and anterior margins t. following a 



-emielliptic curve: free edges grooved, the true contact m.nu'in- >"\ \>\ a 



