PLATE IV. 
Legend, x. Composite laterals. F. Foramen. 
c. Composite centrals. P. Pedicle-groove, 
cd. Cardinal ridge. , , S. Sipho. 
KEY S ERLINGI A, Pander. 
Page 117. 
Keyserlingia Buchi, Verneuil. 
Fig. 1. The interior of a pedicle-valve ; showing the depressed or broadly grooved cardinal area, perfor¬ 
ated by the opening of a sipho which is blind at its inner termination. 
Fig. 2. The interior of a brachial valve; showing a blind internal tube, which is represented as broken, 
the cavity appearing in cross section. 
Fig. 3. The exterior of the pedicle-valve; showing the slit-shaped opening of the pedicle-passage. 
Obolus beds. River Ischora, Russia. 
The above figures are copies of those given by Pander (Bull, de l’Acad. Imp. des Sciences de St. 
Petersbourg, vol. iii, p. 46, pi. ii, figs. 1, h, c, a), and represent the peculiar features assigned 
by him to the genus. The views are considerably enlarged. 
HELMERSENIA, Pander. 
Page 119. 
Helmersenia, sp. ? 
Fig. 4. The interior of a pedicle-valve. The cardinal area is broad and bears 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, according to Pander, is 
atrophied and blind. 
These figures are also taken from the work of Pander cited above (figs. 2 d and b, respectively), 
and the fossils are from the same beds as those of Keyserlingia. 
IPIIIDEA, Billings 
Page 97. 
IPHIDEA Cllf.? ORNATELLA, LillliaiSSOll. 
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 3. 
Fig. 7. Profile of the same; showing the height and curvature of the posterior ridge and its-basal eleva¬ 
tion. X 3. 
Tonto group. Grand Canon, Arizona. 
Iphidea Bella, Billings. 
Fig. 8. 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 restored 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, Vemnont. 
