274 ILLINOIS ACADEMY OF SCIENCE 
Pygidium depressed convex, broadly triangular in outline, 
with entire margin, length a little less than that of the thorax, 
antero-lateral portions sub-angular, lateral and posterior mar- 
gins rounded. The axis but slightly more elevated than the 
lateral lobes, a little less than one-third the width of the py- 
gidium anteriorly, narrowing gradually to the posterior ex- 
tremity. Segments of axis 7 to 9, well defined except in the 
posterior portion, lateral lobes with 7 visible segments which 
arch backwards and reach the margin, without furrows, the 
proximal portion of the anterior segment. concealed by the 
posterior thoracic segment. The surface of the test without 
visible tubercles or other ornamentation. 
The length of an average specimen is 11.5 mm., width 8 
mm., length of cephalon 5 mm., length of thorax 3.5 mm., 
iength of pygidium 3 mm. Fragments of the test of this 
species are numerous in the fine grained sandstone near the 
base of the Thebes formation, near Thebes, where it is asso- 
ciated with Jsotelus brevicaudatus. It also occurs along Madi- 
ison Creek in Calhoun County, Illinois and near Dover Church, 
in Pike County, Missouri. 
EXPLANATION OF PLATE I. 
Hebertella lineolata n. sp. 
Fig. 1. View of ventral valve of type specimen. 
Fig. 2. View of dorsal valve. 
Natural size, Fernvale limestone. 
Endymionia bellatula n. sp. 
Fig. 3. Dorsal view of nearly complete test of type specimen. X 2. 
Thebes sandstone. 
Strophostylus ornatus n. sp. 
Fig. 4. View of nearly perfect specimen. 
Fig. 5. Lateral view of a larger shell. 
Natural size, Orchard Creek shale. 
Isotelus convexa n. sp. 
Fig. 6. Dorsal view of cranidium of type specimen lacking the free 
cheeks. 
Fig. 7. A single free cheek of small individual. 
Fig. 8. Dorsal view of pygidium of about average size. Natural 
size, Thebes sandstone. 
Lingula ovoides n. sp. 
Fig. 9. View of ventral valve of type specimen. X2, Thebes sandstone 
Conularia ornata n. sp. 
Fig. 10. Lateral view of an incomplete specimen, natural size, Thebes 
sandstone. 
