PLATE III. 



Fig. 1. DeUodua MercuHi, Newb., apper surface \ i;^7 



!"■ " " Newb., side view 137 



Coal-Measures, Santa F6, N. Mex. 



FiG. 2. FtychodM Whipplex } Marcon, upper .surface 1M7 



'-'"• '' Marcon, side view 137 



'-'''• '" Marcon, anterior face 1:57 



'-'''-''/■ " Marcon, side and front view of small teeth 137 



Middle Cretaceoi B, Pagosa, Southwestern Colorado. 



I'm;.::. Pi'o&uclw rodo8U8, Newb., ventral valve l.in 



:: ''- " Newb., side view _ _ | 1(( 



8*, 3c. " Newb., specimen with narrow hinge Mil 



•'''• • " " Newb., specimen with broad hinge lin 



(oal Measures, Santa IV, N. Mex. 



Fig. I. Tlettrofomaria excetea, Newb., side view iaq 



! «- " '■ Newb., basal aspecl l.jo 



Carboniferous Btrata, Canon of Colorado River, Southeastern Utah. 



FiG. 5, Spiri/er Texanns, Meek, Bide view, natural size I;..) 



5a. A dorsal view of same specimen, showing cardinal area and foramen ];$<) 



56. A ventral view of a larger specimen, showing the deep angular mesial sinus i;>;i 



