PLATE IV. 



Leg-end. x. Composite laterals. ?. Foramen. 



c. Composite centrals. P. Pedicle-groove, 



cd. Cardinal ridge. S. Sipho. 



KEYSERLINGIA, Pander. 



Page 117. 



Keyseelingia Buchi, Venieuil. 



Fig-. 1. The interior of a pedicle-valve ; sho-wing the depi-essed or bi-oadly gi-ooved cai'dinal ai-ea, perfor- 

 ated by the opening of a sipho -which is blind at its inner termination. 

 Fig. 2. The interior of a brachial valve ; sho-wing a blind internal tube, which is represented as broken, 



■the cavity appearing in ci'oss section. 

 Fig. 3. The exterior of the pedicle-valve ; showing the slit-shaped opening of the pedicle-passage. 

 Obolus beds. Miver Ischora, Russia. 

 The above figures are copies of those given by Pander (Bull, de I'Acad. Imp. des Sciences de St. 

 PetersViourg, vol. iii, p. 46, pi. ii, figs. 1, h, c, a), and represent the peculiai- features assigned 

 by him to the genus. The views are considerably enlarged. 



HELMERSENIA, Pander. 



Page 119. 



Helmersenia, SJ). ? 



Fig. 4. The interior of a pedicle-valve. The cardinal area is broad and beai'.s a median depression or 



deltidium, as if for the passage of the pedicle. 

 Fig. 5. The exterior of a similar valve ; showing the apical aperture which, accoi-ding to Paxdkr, is 



atrophied and blind. 

 These figures iire also taken from the work of Pander cited above (figs. 2d and b, respectively), 



and the fossils are from the same beds as those of KETSEKLrNCUA. 



IPHIDEA, BiLLixGS. 



Page 97. 



Iphidea ciif.? ornatella, Liiuiarssoii. 



Fig. 6. A pedicle-valve, somewhat imperfect about the anterior margin, but showing the subapical area 

 and the very broad cardinal ridge ("pseudo-deltidium." Billings). X S. 



Fig. 7. Pi-ofile of tie same ; showing the height and curvature of the posterior ridge and its basal eleva- 

 tion. X 3. 



Tonto group. Crrand Canon, Arizona. 



Iphidea bell,a, Billings. 



Fig. S. A pedicle-valve in which the subapical area is relatively small; showing the prominence of the 

 cardinal ridge and the position of the foramen, which is not altogether distinct in the speci- 

 men. The figure is also slightly restoi-ed about the edges where the original is somewhat 

 broken. X 3. 



Fig. 9. Three-quarter view of the same, giving the elevation of the shell and the size of the cardinal 

 ridge. X 3. 



Georgia group. Georgia, Vermmit. 



