I'LATE IV I— Continued. 

 I'HOI.IDOrS SUBTRUXCATA, Hall. 

 V\g. 19. Tlip extei-ior of an individual; sliowinfr the slightly Hattened iiosterior slope and faint median 

 ang'uhitiori. X 4. 



Hudson River gronp. Lorraine, N. T. 



PlIOIJDOP.S OVAI.I.S, Hall. 

 Fig-. 20. The externa! surface ; showing the characteristic outline and subcentral apex. X 6. 

 Niagara group. Wald7-ou, Indiana. 



PllOLIDOP.'^ .stjUAMlFORMIi;, Hall. 

 Fi^'. 21. The interior of a large ventral (ij valve ; showing the chai'acter of the muscular area, the median, 

 anterior ad<iu('tor, loUed posterior adductor, and pai-ietal imjiressions. X 5. 

 Niagara grouj). Hamilton, Ontario. 



Pholidoi'S ovata, Hall. 



Fig. 22. An internal cast of a dorsal (!) valve ; showing the sharply defined anterior and posterior ad- 

 ductors, and the parietal scar. X 6. 

 Fig. 23. The interior of the oppo.site valve ; showing the relatively small size of the nui.scular area. X H. 

 Lower Helderberg gi-ouj). Near Clark-niiUe, N. Y. 



Pholidoi'S arenaria, Hall. 



Fig. 24. An intei-nal <!iust of a dorsal (() valve. Prom the oi-iginal specimen. X 2. 

 Oriskany sandstone. Knox, N. Y. 



Pholidops areolata. Hall. 



Fig. 25. An internal cast of the ventral (!) valve. X 3. 



Schoharie grit. Near Clarksville, N. Y. 

 Fig. 26. An internal cast of the opposite valve. X 3. 



Schoharie grit. Knox, N. Y. 



Phoijdop.s patina, S\). IIOV. 



Fig. 27. The extei'ior of a valve ; showing the lamellose growth-lines, ci-ossed l)y fine, interrupted, radiat- 

 ing sti-iiP. Di-awn from a gutta-percha cast of a natural moidd in ileconiposed chert. X 4. 

 Fig. 28. The interior of a doi'sal (?) valve. Fi-om a gutta-percha cast. X 4. 

 Fig. 29. The interior of tlie opposite valve. X 4. 



Corniferous limestone. Dt Ceioville, Ontario. 



PlIOLIDOP.S CALCEOLA, Sp. llOV. 

 Fig. 30. The interior of a dorsal (',) valve ; shewing the tei'uiina! beak and snbajiical ai'ea, and the character 

 of the musculai' impressions. X 12. 



Corniferous limestone. Falls of the Ohio. 



PHOLinop.s Hamiltoni.k, Hall. 



Fig. 31. The exterior of the shell. X 4. 



Fig. 32. Profile of the same specimen showing the valves in conjunction. X 4. 



Hamilton grou)i. Western New YorJc. 

 Fig. 33. The interior of a ventral (?) valve ; sliowing the character of the muscular impressions. X S. 

 Fig. 34. The interior of the opposite valve ; showing the muscular and parietal .scars. X 4. 



Hamilton group. Canandaigna Lake, N. Y. 



PHOLII)OP8 LINGULOIDES, Hall (?). 

 Fig. 35. The interior of a dorsal (?) val\e; showing the tei'uiinal and slightly deflected Ijeak, the subapical 

 area, and the character of the muscular scars. X 2. 

 Hamilton group. Jiii/htitn Mile Creek, N. Y. 



Pholidops oblata, Hall. 



Fig. 3(). An internal cast of the dorsal (.') valve, with two deep anterioi- adductoi- sc:ai-s, the posterior ad- 

 du<:tors lieing very faintly developed, as in the preceding figure. This and figure 35 may 

 I'cpresent the same species. X 4. 



Hamilton group. Oarter'.l MilLs; N. Y. 



l^iiOLiDOPR, L'oiiiparc P. Ha.miltonle. 



Kisr. 37, The extei'ior of the shell ; showinir the form .■uid nutiiije. X >>■ 

 Ue.lford sli.'.les. linlfin-d. Ohio. 



