PLATE IV d. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Legend, a. Deltidium. 
b. Deltidial slope, 
cc. Cardinal area, 
eg. Cardinal groove, 
cr. Crescent, 
d. Areal borders. 
i. Umbonal chambers. 
j. Platform. 
m. Median scars. * 
n. Anterior scars. 
o. Lateral scai-s. 
p. Postmedian scars. 
q. Crown of crescent. 
r. Side of crescent. 
u. Pallial sinuses or ridges (?). 
MONOMERELLA, Billings. 
Page 40. 
Monomerk.lt.a Kingi, sp. 110 V. 
1. An internal cast of a pedicle-valve; showing the very short umbonal chambers and the sharply 
defined muscular impressions. 
2. The opposite side of the same specimen ; showing the internal characters of the brachial-valve. 
Niagara limestone. Hawthorne, Illinois. A*, . 
Monomerella, sp. ? 
3. The inner side of a specimen retaining the shell, believed to be a brachial valve of some species 
of this genus. This specimen is considered by Whiteaves as the pedicle-valve of Rliinoholus 
Galtensis, Billings. Should Mr. Whitbaves’ opinion prove correct, it will probably be neces¬ 
sary to remove Billings’ species to some other genus. 
4. The exterior of the same specimen. 
Guelph limestone. Galt, Ontario. 
Monomerella Greenii, sp. nov. 
5. An internal cast of a pedicle-valve ; showing the extremely small umbonal chambers and the 
sharply defined crescent, cardinal groove and lateral scars. 
Niagara limestone. Grafton, Wisconsin. 
6. An interior cast of the brachial valve ; showing a portion of the broad area of contact, the plat¬ 
form scars, with the diverging anterior ridges. 
Niagara limestone. Rising Sun, Ohio. 
7. The interior of a brachial valve, from a gutta-percha cast of a natural impression. The crescentic 
fulcrum is exceedingly strong and the platform very obscure. 
8. An internal cast of a pedicle-valve ; showing the very broad cardinal margin and its lateral exten¬ 
sion ; also the faint umbonal cavities and the conspicuous cardinal groove and crescent. 
9. The interior of a brachial valve, with sharply defined terminal scai-s and anterior ridges. From 
a gutta-percha cast. 
10. An internal cast of a brachial valve ; showing,_ in the matrix, the impression of the cardinal area. 
* The platform scars are accompanied by scarcely any thickening of the shell. 
Niagara limestone. Gh’afton, Wisconsin. 
Monomerella ovata, var. lata, Whiteaves. 
11. The exterior of a pedicle-valve. From the original specimen figured by Whiteaves (Palaeozoic 
Fossils, vol. iii, pt. 1, pi. 2, fig. 2a). 
12. A portion of the interior of a pedicle-valve. From Whiteaves’ original (op. cit., pi. 8, fig. 2). 
Guelph limestone. Durham, Ontario. 
Monomerella ovata, Whiteaves. 
13. View from the brachial side of a fine specimen retaining the valves in conjunction. 
14. Profile of the same. From Whiteaves’ original specimen (op. cit., pi. 8; figs. 1, la). 
15. The interior of a pedicle-valve; showing the broad cardinal area and deltidial slope, the shallow 
umbonal chambers, the deep cardinal groove and lateral scars of the crescent, anil the slightly 
elevated anterior edge of the platform. From Whiteaves’ original specimen (op. cit. pi. 8, 
fig. 16). 
Guelph limestone. Durham, Ontario. 
