EXPLANATIONS OF PLATE II. 



PAGE 



Fig. 1. a, b, c. . . . Chvenomya leavenworthensis. 43 



1 a. Side view, with portions of the shell removed, so as to show the muscular scars, and faintly 

 sinuous pallial impression. 



1 b. Dorsal view of au internal cast, showing the wide posterior gap. 



Fig. 2. a, b Ch^nomya Cooperi 44 



2 a. Side view of a cast, with a little of the posterior margin broken away. 



2 b. Dorsal view of same, showing a distinct depression along the hinge left by an internal thicken- 

 ing of the cardinal margin. 



Fig. 3. .... Pleurophorus ? subcuneata 61 



Fig. 4. a, b Yoldia subscitula. .... 60 



4 a. Side view of a cast, left valve. 



4 b. Dorsal view of same. 



Fig. 5. a, b, c Eumicrotis Hawni 54 



& a. Internal cast of a left valve (ribs obscure). 

 .') b. Profile anterior view of a left valve. 



5 c. Internal impression of a right valve showing the deep byssal sinus at (s). 



Fig. 6. a, b. . . . Eumicrotis Hawni, var. ovata. ..... 55 



6 a. Cast of the exterior surface of a left valve, showing the very short hinge line, and distinct 



costae of this variety. 



6 b. Anterior profile view of same. 



Fig. ^. a,b, c Myalina permiana. 52 



7 a. Internal cast of a left valve, usual form. The impression of the hinge area shown in outline 



in this figure, is added from another specimen. 

 7 b. Anterior view of same. 



7 c. Cast of a broader variety of same species not showing the cardinal area. 



Fig. 8. a, b, c, d. . . . Myalina aviculoides. 51 



8 a. Cast of the exterior of a left valve, adult size. 

 8 h. Anterior view of same. 



8 c. Cast of exterior of a young specimen. 

 H d. Anterior view of same. 



Fig. 9. . . . AvicuLOPECTEN McCoYi, (ext. cast left valve) 50 



Fig. 10. . . . AvicuLOPECTEN ? (cast left valvc). .... 50 



Fig. 11 a, & SCHIZODUS OVATUS 59 



11 a. Cast, left valve, side view, 

 lift. Dorsal view of same. 



Fig. 12. a, 6 Bakevellia parva 57 



12 a. Cast of left valve, side view, natural size. 



12 6. Cast of another specimen enlarged. 



Fig. 13. a, b. . . Pleurophorus Caliiouni. ...... 62 



13 a. Internal cast, side view, showing a cast of the anterior muscular impression, with a furrow 



behind it, left by an internal ridge. 



13 6. Dorsal view of the same, being a cast of the interior of the two valves as seen partly opened. • 



Fig. \i. a, b Nautilus eccentricus. ... .05 



14 a. Side view of an internal cast, showing the septate and non-septate portions 

 14 6. Dorsal view of same. 



