PLATE IV I— Continuoil. 

 I'lIOI.IDOI'S SUBTRUNCATA, ILlll. 

 Kig. 19. 'J"ht» exterior of an indiviilual ; sliowiiif,' tlie slightly tiattened posterior slope and faint median 

 angulation. X 4. 



Hudson River group. Lorraine, N. Y. 



PlIOI.IDOP.S OVAI.IS, ll:ill. 

 Fig. 20. The external surface ; showinj,' llie characteristie mitline and subcentral apex. X C. 

 Niagara group. Wahlnm, Indiana. 



PlIOI-IDOl'.s S<iUAMII-ORMr5i. TTmII. 

 Fi". 21. The interi(U- of a large ventral (!) valve ; showing the character nf the muscular area, the median, 

 antericu' adductor, lolied posterior ad<luctoi-. anil jiarietal impressions. X i>. 

 Niagara group. HnmUtoii, Ontario. 



Pholidops ovata, Ilall.. 

 Fig. 22. An intei-nal cast of a doi-sal (!) valve ; showing the sharply defined anterior and posterior ad- 

 ductors, and the parietal scar. X 6. 

 Fig. 28. The interior <if the oppo.site valve ; showing the relatively small size of the muscular area. X t!. 

 Lower Helderberg group. Near Clarksnille, N. Y. 



PlIOLIDOPS ARENAltIA, ILlll. 

 Fig. 24. An internal cast of a dorsal (0 valve. From the oiiginal specimen. X 2. 

 Oriskany sandstone. Kno-r, N. Y. 



Pholiijop.s aueolata. HmII. 



Fig. 25. An internal cast of the viMitral (0 valve. X 3. 



Schoharie grit. Near Olarksville, N. Y. 

 Fig. 26. An intei-nal cast of the opposite valve. X 3. 



Schoharie gi-it. Knox, N. Y. 



Pholidop.s patina, .sp. nov. 



Fig. 27. The exterior of a valve ; showing the lamellose growth-lines, crosseil by fine, interrupted, radiat- 

 ing stria>. Drawn from a gutta-percha cast of a natural mould in decompo.sed chert. X 4. 

 Fig. 28. The interior of a dorsal ('() valve. From a gutta-pei'cha cast. X 4. 

 Fig. 29. The interior of the ojiposite valve. X 4. 



Corniferous limestone. De Cemville, Ontarin. 



Pholidop.s calceola, sp. nov. 



Fig. 30. The interior of a dorsal (f) valve ; shewing ihe terminal beak and subajiical area, and the charactei- 

 of tlie muscular impi'essions. X 12. 



Coi'niferous limestone. Falls nf the Ohio. 



Pholidop.s Hamilton:.*, Hall. 



Fig. 31. The exterioi-of the shell. X 4. 



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



Hamilton group. IVestern New York. 

 Fig. 33. The intei'ior of a ventral (?) valve ; showing the charactei- of the nuiscular imiiressions. X S. 

 Fig. 34. The interior of the ojiposite valve ; showing the mu.scular and parietal scars. X 4. 



Hamilton group, Canaiulaigua Lake, N. Y. 



PlIOLIDOPS LINGULOIDES, Hilll (?). 

 Fig. 3."). The interior of a dorsal (f) valve; showing the terminal an<l slightly detlecled beak, the subapical 

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

 Hamilton group. Eighteen Mile Creek, N. Y. 



PlIOLIDOPS oblata, Hall. 

 Fig. 3G. An internal ca.st of the dorsal (0 valve, with two deep anterior adductor scars, the posterior ad- 

 ductoi-s being veiy faintly developed, as in the preceding figure. This and figiiie 35 may 

 represent the .same species. X 4. 



Hamilton group. Carter's Mills, N. Y. 



PlIOLIDOPS, compare P. IIa.miltoni.e. 



Fi" 37. The extei'ior of the shell ; showing the form and outline. X 0. 

 ISedford ^hnles. Beilfont. ";,;„. 



