PLATE III. 
Fig-. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig- 
Legend. 1. Laterals. 
c. Centrals. 
sc. Subcardinals or postmedians, 
cr. Crescent, 
e. Externals, 
x. Composite posteriors. 
P. Pedicle-groove. 
F. Foramen. 
f. Foraminal pits, 
s. Septum (median), 
s'. Septum (lateral), 
o. Vascular trunks (oviducts?). 
d / . Subapical area, 
cb. Cardinal bosses, 
fc. Foraminal callosity. 
LEPTOBOLUS, Hall. 
Page 73. 
Leptobolus insignis, Hall. 
1. An internal cast of a pedicle-valve ; showing the long, curved lateral scars and a faint indication 
of the posterior muscular depression. X 10. 
2. An internal cast of the brachial valve, similarly enlarged, and showing the median septum and 
two lateral grooves, which correspond either to the scars (z) seen in fig. 6, or to the lateral septa 
(s') in fig. 10. 
Utica slate. Holland.Patent, N. Y. 
3. The exterior of the shell; showing the concentric and radiating strite. X 8. 
Utica slate. Middleville, N. Y. 
4. The interior of a pedicle valve ; showing the cardinal area and groove, and the thick, calloused 
fulcra of the lateral muscles. X 15. 
5. Another interior of this valve, in which the transverse extensions of the lateral fulcra are continu¬ 
ous. The posterior depressed area bears the impression of the central muscles, and indications 
of a subdivision of the pitted surface into differentiated scars. X 15. 
6. The interior of a brachial valve ; showing the grooved area, conspicuous median septum and faint 
lateral scars. 
Hudson River group (Utica horizon). Covington, Kentucky. 
Leptobolus occidentalis, Hall. 
7. The exterior of the shell. X 8. 
Dark shale of the Utica horizon. Hawley's Mill, 12 miles north-west of Dubuque, Iowa. 
Leptobolus lepis, Hall. 
8. The interior of a pedicle-valve ; showing the cardinal groove and the diverging septa. X 12. 
9. A cast of the interior of the pedicle-valve ; showing the central scar and the transverse extension 
of the laterals. X 12. 
10. The interior of the brachial valve ; showing the grooved cardinal area and the median and latera 
septa, each of which is bifurcate at its extremity. X 12. 
Hudson River group. Licking River, Ohio. 
SCHIZOBOLUS, Ulrich. 
Page 87. 
SCHIZOBOLUS TRUNCATUS, Hall (sp.). 
11. The exterior of a pedicle-valve. X 3. 
Genesee slate. Western New Yoi'k. 
12. The interior of a pedicle-valve, drawn from one of Mr. Ulrich’s original specimens; showing the 
pedicle-slit, the composite muscular scars abutting against the median septum, and the long, 
curved lateral scars'. X 5. 
Black slate (Genesee). Madison county, Kentucky. 
13. The exterior of the brachial valve. X 3. 
Genesee slate. Western New York. 
14. The interior of the brachial valve ; showing the septum and faintly defined muscular impressions. 
X 5. 
Black slate (Genesee). Madison county, Kentucky. 
