PLATE IV c;— Continued. 

 TlJEMATIS OIU.AIA, Ulliill. 



FifT. 20. The liiai-hial valvp, ri'tainiiitr a portion ni' the external ornanientatinn. X 2. 

 Fi-nm a gutta-jiei-cha cast of the original siiecimen (op. cit., tig. 19). 

 Hudson River group, dndnnati, Okin. 



SCIIIZOCKANIA, Hall mikI Whitfield. 



I'.ige ItJ. 

 SCHIZOCRANIA (?) KLDl.-<, ll.lll. 

 Fig. 21. The exterior of the bi-achial valve. X 2. 



Trenton limestone. Clifton, Teiin. 



SCHIZOCRAMA FILOSA, Hall. 



Fig. 22. The exti'rior of a brachial valve, attached to Straphomena alteriiala. X 2. 



Huilson River group. Cincinnati, Ohio. 

 Fig. 23. The exterior of a hirge Itrachial valve. 

 Fig. 24. The pedicle-valve. 



Utica slate. Mohawk Valley, JV. Y. 

 Fig. 2.5. A valve of Strophmnena alteniata, to which five of these shells are attached, all of them exiwsing 

 the lower valve. 

 The figure is taken from the. Palaeontology of Ohio, vol. ii, pi. i. tig. 12, and the muscular .^cai-s on 

 the internal cast of the up]>er valve, shown in the left of the illustration, remain as there i-ep- 

 resented. 

 Fig. 26. An internal cast of the brachial valve ; showing the elongate, converging posterior seal's, separat€<i 

 into posterior and anterioi' elements; also a faint median ridge extending forward beyond the 

 muscular impressions. X 3. 

 Fig. 27. The i>edicle-valve seen on the right nuirgin of tig. 25 ; showing the apical pedicle-callosity or 

 incipient groove. X 2. 

 Palaeontology of Ohio, vol. ii, pi. i, lig. 15. 

 Fig. 28. The pedicle-area viewed fi'om within ; showing more accurately the character of the apical cal- 

 losity, its median ridge and lateral walls indicating homology with the corresponding part.s in 

 the genus Obbicdloidka X 3. 



Hudson Rivei' group. Cinvinnati, Ohio. 

 Fig. 29. An inili\'idual from which the ujiper portion of the brachial valvi; 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 3.">, the <liameter of the 

 lower valve is less than that of the upper, and the former lies above ami within the ba.-<e of the 

 lattei-, the attachment of the shell lieing lai-gely effected by the marginal portions of the larger 

 valve. 



Hudson Rivei' group. Covington, Ky. 

 Fig. 30. An internal cast of a brachial valve ; showing the anterior and posterior muscular scars. The 

 former impre.s.'^ions are rarely discernible. X L5. 

 Ti'enton limestone. Trenton Falls, N. Y. 



SCHIZOCRANIA SCHUCHEKTI, !<p. IIOV. 



Fig. 31. A brachial valve, retaining a poi'tion of the extenial ornamentation, but showing the posterior 



muscular scai-s. X 3. 

 Fig. 32. A smaller brachial valve, retaining most of the exterior sui-face. X 3. 

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



The features of the pedicle-area ai-enot so clearly retained as to allow delineation. X 3. 

 Hudson Rivei- group. Comngton, Ky. 



SCHIZOCRANIA (?) HeLUEKBERGIA, HYi. UUV. 

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

 coticentric striation, and the overlapping edges of the finely striated upper valve. The character 

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

 Fig. 35. The internal surface of the jiedicle-valve ; showing what appeal's to bo a broad pedicle-fis.sui'e, 

 and the overlapping margins of the upper valve. X 3. 



Lower Heldprl)ertr group. Near Clarksvillc, N. Y. 



