PLATE IV G— Continued. 



Trematis oblata, Ulrich. 



Fi{i'. 20. The brachial valve, vnttiming a portion of tVie extei'iial oriianientation. X 2. 

 From a gutta-peroha cast of the original specimen ((qy. vit., fig. 19). 

 Hudson Rivei' group. Cincinnati, Ohio. 



SCHIZOCRANIA, Hall mikI Whitfield. 



SCHIZOCRANrA (?) RUDIS, Hall. 



Fig. 21 . The exteiior of the bi'achial valve. X 2. 



Ti'enton liniestone. Clifton, Tciin. 



SCHIZOCRANIA FILOSA, HilU. 



Fig. 22. The extei-ioi- of a brachial valve, attached to Strophumeyia alteriuita. X 2. 



Hudson River gi'oup. Cincinnati, Ohio. 

 Fig. 23. The extei-ioi- of a large lirachial valve. 



Fig. 24. The pedicle-valve. 



Utica slate. Mohawk Valley, N. T. 

 Fig. 2.'). A valve of Strophomeiia altei-nata, to which five of these shells are attached, all of them exposing 

 the lower valve. 

 The figui-e is taken fi-oni the Paljeontology of Ohio, vol. ii, pi. i, fig. 12, and the muscular scai-s on 

 the internal cast of the upi)er valve, shown in the left of the illusti-ation, remain as there rep- 

 resented. 

 Fig. 26. An internal cast of the brachial valve ; showing the elongate, converging posteiioi- scars, separated 

 into postei-ioi- and anteiior elements; also a faint median ridge extending forward beyond the 

 muscular impi-essions. X 3. 

 Pig. 27. The pedicle-valve seen on the light margin of fig. 25 ; showing the apical pedicle-callosity or 

 incipient groove. X 2. 

 Paleontology of Ohio, vol. ii, pi. i, fig. 1."). 

 Fig. 28. The pedicle-area viewed from within ; showing more accurately the charactei' of the apical cal- 

 losity, its median ridge and latei'al walls indicating homology with the corresponding pai-ts in 

 the genus Orbiouloidea X 3. 



Hudson Rivei' group. Cincinnati, Ohio. 

 Fig. 29. An individual from which the upper portion of the brachial valve has been removed, exposing all 

 the internal characters of the pedicle-valve. X 2. 

 It will be obsei-ved that in this figure, as well as in figs. 25, 33, 34 and 35, the diaraetei- of the 

 lower valve is less than that of the upper, and the former lies above and wdthin the base of the 

 lattei-, the attachment of the shell being largely eflFected by the marginal portions of the larger 

 valve. 



Hudson Rivei' gi-oup. Covington, Ky. 



Fig. 30. An intei-nal cast of a brachial valve ; showing the anteiior and posteiior muscular scars. The 

 former impressions are rarely discernible. X 1-5. 

 Trenton limestone. Trenton Falls, N. Y. 



SCHIZOCRANIA ScHUCHERTI, S^). IIOV. 



Fig. 31. A bi-achial valve, retaining a portion of the external ornamentation, but showing the posterior 



muscular scars. X 3-' 

 Fig. 32. A smaller brachial valve, retaining most of the exterior surface. X 3. 

 Fig. 33. An individual from which most of the upper valve has been removed, exposing the pedicle-valve. 



The features of the pedicle-area are not so clearly retained as to allow delineation. X 3. 

 Hudson River group. Covington, Ky. 



SCHIZOCRANIA (?) HeLDERBERGIA, sp. llOV. 



Fig. 34. The exterior surface of an individual ; showing the pedicle-valve, its coai-sely radiate and obscure 

 concentric striation, and the overlapping edges of the finely sti'iated upper valve. The chai'acter 

 of the pedicle-aperture is not well retained. X 2. 



Fig. 35. The internal surface of the pedicle-valve ; showing what appears to be a broad pedicle-fissure, 

 ., , ami the overlapping margins of the upper valve. X 3. 

 ' ■' Lower Helderbei'g gi'oup. Near Clarks-ville, N. Y. 



