185 



margin ; 



marginal 



Fig. 85. Schizobolus truncatus. Interiors of pedicle and 



notch in pedicle 

 (lower) valve; and 

 concentric striae. 

 Found i n t h e 



fig. «5. Schizobolus truncatus. Interiors or pecli 

 black X('ll)leS Shales brachial valves, showing median septum Hanked by callosity 

 1 ' in each; exterior of pedicle valve, x 2%, upper Moscow 



o +• Stur2"eOn Point * ( transition ) Shales; eighteen Mile Creek. (Original.) 



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

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

 Orbieuloidea media 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. 



[Ety. : Kranion, upper part of a skull.] 



(1781 : Scbriften der Berliner Gesellschaft Nfaturforschender Freunde. 

 Bd. II., p. 72. 1892: Pal. K Y., Vol. VIII. , Pt. I., p. 145.) 



Shell with valves unequal, not articulated, 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 surface 

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

 near the center; often strongly marked muscular impres- 

 sions. 



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

 IX., p. 28, PL III.) 



Distinguishing Characters. — Nearly circular 

 outline; low conical form; smooth apex; 

 sharp, elevated and crenulated striae, which \ 



radiate from the apex, and are increased 

 in number by the appearance of new ones ' - 



between the diverging older ones. fig. 86. crania 



° ° crenistriata. Later- 



Found in the "Hamilton group, in Eight- ai and top views of an 



& l ° elliptical dorsal 



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

 attached to Cystiphyllum in the Demissa bed, at Sec- 

 tion 5. 



■'*■•■■../:>.£ 



