EXPLANATIONS OF PLATE II. 



PAGE 



Fig. 1. a, b, c. . . CH^NOMTA LEAVENWORTHENSIS. . . .43 



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

 sinuous pallia! impression. 



1 6. Dorsal view of an internal cast, showing the wide posterior gap. 



Fig. 2. a, b. . . . . CH^ENOMYA 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. .* . . fil 



Fig. 4. a, 6 YOLDIA SUBSCITULA. . .... CO 



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). 



5 6. 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 



costse of this variety. 



6 6. Anterior profile view of same. 



Fig. 7. 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 6. 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 b. Anterior view of same. 



8 c. Cast of exterior of a young specimen. 

 8 d. Anterior view of same. 



Fig. 9. ... AVICULOPECTEN McCoTi, (ext. cast left valve) 50 



Fig. 10. ... AVICULOPECTEN ? (cast left valve). ... 50 



Fig. 1 1 a, b. . . . . SCHIZODUS OVATUS 59 



11 a. Cast, left valve, side view. 



11 b. Dorsal view of same. 



Fig. 1 2. a, b ^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 CALHOUNI G2 



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



Fig. 14. a, b. . . . . NAUTILUS ECCENTRICUS. ... . C5 



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

 14 b. Dorsal view of same. 



