185 



margin; marginal 

 notch in pedicle 

 (lower) valve; and 

 concentric striee. 



Fonnd in the ^ „ „ , . ^ , ^ ^ ,, . , ,. , 



Fig. 85. Schizobolus truncatus. Interiors of perncie ana 

 black Naples shales, !irachial valves, showing median septum flankt-a by ,;iillosity 

 i ' m each; exterior of pedicle valve, x S-.;, iipiicr Moscow 



r. J- Sfninvpon T*oillt* (t'"aiisition) shales; eighteen Mile Creek. ^Original.) 



in the npper Moscow shales (transition beds) and down to 

 fonr feet from the top, at Sections 1, 2, 3, 4; and in the 

 Orbiculoidea niedhi bed of the middle Moscow shale, at Sec- 

 tions 4 and 5. 



Measurements. — Length G.2 mm.; width 5.7 mm. average. 



Genus CRANIA. Retzius. 



[Ett. : Kranion, iijiper i)art of a skull.] 



(1781: Scliriften der Berliner Gesellschaft Naturforscliender Freunde. 

 Bd. II., p. 72. 1892: Pal. X. Y., A"ol. VIII., Pt. I., p. 145.) 



Shell with valves nnecpiid. not articnlated, and without 

 perforation for the pedicle: attached by the apex or the 

 entire surface of the lower valve; lower (attached) valve 

 with apex slightly elevated if not conforming to snrface 

 to which it is attached ; npper valve conical, with apex 

 near the center; often strongly marked mnscnlar im[)res- 

 sions. 



Crania ckenistkiata. Hall. (Fig. 86.) Pal. N. Y., Vol. 

 rV., p. 28, PL III.) 



Distinguishing Characters. — Nearly circular 5;^ 



outline; low conical form; smooth apex; 

 shjirp, elevated and crennlated stritTS, which 

 radiate from the apex, and are increased 

 in number by the appearance of new ones 

 between the diverging older ones. 



Found in the "Hamilton grouii, in Eight- ai ami top views of an 



*=" 1 '^ elliptical dorsal 



een Mile Creek." (Hall, type.) The shell is vaive (from Haii). 

 attached to Cystiplndlum in the Demissa bed, at Sec- 

 tion 5. 



'^ 



Fig. 86. Crania 

 crcnistriata. Later- 



