PLATE IV. 



Legend. x. Composite laterals. F. Foramen. 



c. Composite centrals. P. Pedicle-groove. 



cd. Cardinal ridge. S. Sipho. 



KEYSERLINGIA, Pandkh. 



.,. ^^^ ,_ Page 117. 



Keyserhngia Buchi, Vemeiiil. 



Fig. 1. The interior of a pedicle-valve ; showing the depressed or broadly grooved cardinal area, p<!i-for- 

 ated by the opening of a sipho which is blind at its inner tei'mination. 



Fig. 2. The interior of a brachial valve; showing a blind internal tnlie, which is represented as broken, 

 the cavity apjiearing in cross section. 



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

 Oliolus beds. Mivsr Istihora, Russia. 

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

 Petei'sbourg, veil, iii, p. 46, ])1. ii, tigs. 1, h, c. a), and represent the peculiar features assigned 

 by him to the genns. 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 depressinn-or 



deltidium, as if for the jiassage of the pedicle. 

 Fig. 5. The exterior of a similar valve ; showing the apical aperture which, according to PiUDEB, is 



atrophied and blijid. 

 These figures are also taken from the wni-k of Pander cited above (figs. 2 d and b, re.spectively), 



and the fo.ssils are froin the same beds us tho.=;e of Keyserlincua. 



IPlllDEA, Billings. 



' Page 97. 



Iphidea ciif.? ornatella, Liiiiiar.sson. 



Fig. 6. A pedicle-vah'e, somewhat imperfect about the anterior margin, liut showing the subapiival 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. S. A pedicle-valve in which the snbapical area is relatively small; showing the pi'ominence of the 

 cardinal lidge and the position of the foi'amen, which is not altogether distinct in the speci- 

 men. The figure is also slightly restored about the edges where the oi-iginal is somewhat 

 broken. X 3. 



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

 ridge. X 3. 



Georgia group. Georgia, Veniwnt. 



