PLATE 3. 



P»ge 

 Figs. 1, 2. Pholidops ovalis. 



1, 2. Vertical and profile views of a specimen retaining botli valves. From the Niagara ^oup 

 of '^Valdron, Ind. Enlarged to five diameters. 



Fig. 3. Pholidops arenakia (See note on 32) 



A cast of the valve fVom the Oriskany sandstone, enlarged to three diameters. See p. 413. 



Figs. 4, 5. Pholidops akeolata 31 



4. An impression of the dorsal valve. 



5. An impression of the ventral valve. The figures enlarged to three diameters. 



Figs. 6-9. Pholidops hamiltoni.*: 32 



6. The exterior of the shell, enlarged to four diameters. 



7. The interior of ventral valve, showing the muscular impressions. 



8. An impiession of the ventral valve. 



9. The opposite or dorsal valve of the same species, enlarged to eight diameters. 



if.ii. nil Ijluli'l syihV !»lJi(t>. . 



Fig. 10. Pholidops oblata 413 



10. AnimpressionCapparentlyof the dorsal valve), showing the muscular impression; enlarged 



to four diameters. 



Fig. 11. Pholidops i lamellosa 413 



11. Ventral ? valve of the specimen; enlarged to two diameters. 



Fig. 12. CeaNia auroka 27 



12. An impression of a ventral valve. 



Figs. 13-16. Crania crenistriata 28 



13. The dorsal valve of a small individual. 



14. The dorsal valve of a large individual, the margins having been crushed. 



15. Vertical view of a broadly elliptical dorsal valve. 



16. Profile of the same. 



Figs. 17-23. Crania HAHiLTONi.fi 27 



; ! . ..ii. -J irfl 111 li'^ifiirj e07lir/ f/Hlnr/ fcttju f««-n>U 



17. Vertical view of a dorsal valve. 



JL- 



18. Profile of the above. 



'19. Two Iildividuals attached to the surface of a shell of Tropidoleptus, one of them having 

 carried the form of the ribs of the shell into its growth. 



20. The interior of a ventral valve. 



21. A group of ventral valves attached to the surface of Microdon bellastriata. 



22. A ventral valve having the cardinal border modified in its outline by the presence of Spi- 



rorbU angulata a, a, attached to the same shell surface with the Crania. 

 28. An enlargement of the specimen fig. 22,intended to show the muscular and vascular markings 

 more distinctly. 



