470 
THE GEOLOGIST. 
7. Cybha irapeioidalis, Dalman. Interior of the ventral valve, to show that the 
diverging dental or rostral plates are similar to those of Sjnrifera, 
but essentially different from those of Cyrtina. D, pseudo-del- 
tidium ; P, foramen. 
8. „ cmpidata, Martin, viewed in profile, and from which a portion of the 
valves have been removed, so as to exhibit the two diverging 
dental or rostral plates. 
9. Spibifeeina rostrata, Schlotheira, from which a portion of the smaller valve has 
been removed, so as to show the back of the spiral cones, as well 
as the position of the central plate of the larger or ventral valve. 
10. „ rostrata. Interior of the ventral valve, exhibiting the lai'ge ver- 
tical median plate, or septum, to which was attached the adductor 
or occlusor muscle. R, ventral adjuster. The two plates com- 
posing the pseudo-deltidium are here clearly defined. 
11. fivessi\ plicata, E. Deslongchamps. Interior of the dorsal valve, in which 
the cardinal process and largely-developed hinge-plates are well 
exhibited ; no perfect interior of this genus has, however, been 
obtained, so that the spiral appendages could not be represented. 
A good illustration of the larger valve is likewise among the 
desiderata, although some of its characters have been described 
and represented by Mr. E. Deslongchamps. 
12. Cyrtina heteroclyta, Defrance. Interior of the ventral valve, to show the large 
single median septum, to the upper surface of which were 
attached dental or lostral plates ; a small portion of the arched 
pseudo-deltidium has been removed. 
13. „ Demai-lii, Bouchard, to show that in this species t'lo median septum 
extends to the roof of the arched pseudo-deltidium, the dental 
plates being fixed to the sides of the septum, instead of the upper 
edge, as in C. heteroclyta and C. scptosa. Tlic perfect interior 
of the smaller or dorsal valve of no species of Cyrtina has been 
hitherto discovered. 
14. Athtris (M'Coy) = SriRiGERA (d'Orb)^firfOTt/cra, J. de C. Sowcrby. Interior 
of the dorsal valve, and of a portion of the ventral one, magnified. 
The hinge-plate, and its small circular aperture, as well as the 
spirals and their complicated connecting processes, are here repre- 
sented ; but the spiral cone on the right side has been somewhat 
displaced from its natural position in order to better explain the 
connecting system of lamellaB. The hinge of both valves is also 
here seen, as well as the rostral plates and foramen of the larger 
or ventral valve. 
15. „ concent rica, Von Buch. Interior of the ventral valve ; the adductor 
A, and divaricator muscular impressions R, are here clearly 
defined. 
16. Merista Ilercidea, Barrande, to show the shoe-lifter-shaped process H, 
first described by Prof. King. 
17. „ tuniida, Dalman. Interior of the dorsal valve. Although much 
labour has been bestowed by Prof. Suess in working out the 
interior character of his genus, a correct restored representation 
of the interior has still to be produced ; the one here given is not 
sufficiently detailed or precise. 
IS. „ Interior of the ventral valve. 
19. „ scalprum, Rcemer. Exterior of the ventral valve, in which the two 
diverging lines due to the dental plates are seen, as well as the 
hollow under the shoe-lifter process or plate. 
20. RiTziA serpentina, de Koninck, from a drawing by Mr. S. P. Woodward ; no 
perfect representation of the interior of either valve has been 
hitherto produced, and all we know is, that the specimens com- 
posing the sub-genus were provided with spiral processes. 
