0RISKANY FAUNA OF BECKAFT MOUNTAIN 119 



Crania cf. bella Billings 



Page S3 

 Fio. 



19 The upper valve 



20 Profile view of a very young example showing the 



regular conical form. xlO 



Pholidops sp. 



Page 59 



21 The interior of one of the valves 



22 The exterior. x5 



Pholidops terminalis Hall 



Page 5? 



23 The exterior of the larger valve. x3 



24 The interior showing the muscular scars. x3 



25 A valve showing replacement of the shell by a series 



of chalcedonies formed concentrically about centers of 

 silicification 



