PLATE IV b. 
Legend. 
a. Deltidium. 
b. Deltidial slope. 
c. Deltidial ridges, 
ca. Cardinal area, 
cr. Crescent. 
d. Areal borders. 
h. Cardinal buttress. 
i. Umbonal chambers. 
j. Platform. 
k. Platform-vaults. 
m. Median scars. 
n. Anterior scars. 
o. Lateral scars. 
q. Crown of crescent. 
r. Side of crescent. 
t. Transeverse scars. 
u. Pallial sinuses. 
x. Umbo-lateral scars. 
TRIMERELLA, Billings. 
Fig. 
Fig. 
Fig. 
Figs. 
Fig. 
Page 33. 
Trimerella Lindstrcemi, Dali. . 
1. The interior of an imperfect pedicle-valve; showing the deep excavation at the base of the del¬ 
tidium in the place usually occupied by the cardinal buttress. 
Aymestry limestone. Island of Gotland. 
Trimerella grandis, Billings. 
2. An internal cast of a .portion of a small pedicle-valve, i 
3. The opposite side of the same. 
Guelph limestone. Galt, Ontario. 
4. 5. Transverse sections, showing the structure of the platform. 
Trimerella acuminata, Billings. 
6. The interior of a pedicle-valve, somewhat restored about the umbo ; showing the platform, lateral 
scars of the crescent and the excavate cardinal buttress. From a gutta-percha impression of 
a natural cast, 
Niagara limestone. Port Byron, Illinois. 
KH1 NOBOLUS, Hall. 
Page 41. 
Rhinobolus Galtensis, Billings. 
Fig. 7. The interior of a pedicle-valve; showing the narrow deltidium, broad deltidial ridges and the 
small, imperfectly developed platform. The drawing is made from a gutta-percha impression 
of a mould of the interior, the specimen being that originally taken as the type of the genus. 
Guelph limestone. Galt, Ontario. 
Fig. 8. The interior of a small brachial valve. 
Guelph limestone. Elora, Ontario. 
Fig. 9. The interior of a larger brachial valve ; drawn from the specimen figured by Wiiiteaves on plate 
8, fig. 3, Palaeozoic Fossils, vol. iii, pt. 1. 
Guelph limestone. Hespeler or Durham, Ontario. 
Rhinobolus Davidsoni, sp. nov. 
Fig. 10. A small pedicle-valve, showing the internal characters. From a gutta-percha impression of a 
natural cast. 
Fig. 11. The interior of a brachial valve, believed to belong to the same species. 
Fig. 12. The interior of a larger brachial valve; showing the undeveloped platform, the crescent and the 
transverse muscular scars. 
Niagara limestone. Gh'afton, Wisconsin. 
