PLATE XXVII. 
c. Trapezoidal area, including central, middle j. Anterior lateral muscle sear. 
lateral, and outside lateral muscle sears. m. Pedicle muscle. 
g. Umbonal muscle scar. v. Visceral cavity. 
h. Central muscle scar. vs. Main vascular sinus. 
LINGULELLA PRIMA (Conrad MS.) (Hall) (p. 526). 
Fiavre 1. Cast of the interior of a ventral valve, showing the pestle-shaped ridge that filled the median groove of the 
interior of the shell. U.S. Nat. Mus. Cat. No. 27435a. 
la. Exterior ofa ventral valve, showing rather strong undulations of growth. U.S. Nat. Mus. Cat. No. 27435 
1b. Fragment of a ventral valve, showing the cast of the area, the divided umbonal muscle scar (g), and the 
pedicle scar (m). U.S. Nat. Mus. Cat. No. 27435c. 
lc. Partly exfoliated dorsal valve. U.S. Nat. Mus. Cat. No. 27435d. 
The specimens represented are all from Locality 77, Upper Cambrian sandstone, Ausable Chasm, Essex County, 
New York. 
LINGULELLA Iris (Billings) (p. 509). 
Fictre 2. Dorsal valve, the type specimen, from Locality 319d, Upper Cambrian, Point Levis, Quebec, Canada. 
Geol. Survey Canada. Redrawn from the specimen described and figured by Billings [1865a, p. 301, 
fig. 290] as Lingula iris. 
OBOLUS PRINDLEI (Walcott) (p. 409). 
Figure 3. Ventral valve, the type, from Locality 72a, Lower Cambrian, 1 mile southwest of Wynantskill, Rensselaer 
County, New York, showing the character of the outer surface and also of the surface of the inner 
layers where the shell is exfoliated over its umbonal portion. U.S. Nat. Mus. Cat. No. 27333a. 
34. Cast of the interior ofa ventral valve which is broken away a little at the beak. This specimen is associated 
on the same hand specimen with the valve represented in figure 3. U.S. Nat. Mus. Cat. No. 27333b. 
3b. Portion ofa ventral valve from Locality 72a, Lower Cambrian, 1 mile southwest of Wynantskill, Rensselaer 
County, New York, showing the cast of the finely punctate inner surface and the peculiar lamellose- 
like strize of growth upon the area. U.S. Nat. Mus. Cat. No. 27333c. 
3c. Cast of the interior of a dorsal valve, associated on the same hand specimen with the valve represented by 
figure 3, showing the area. U.S. Nat. Mus. Cat. No. 27333d. 
3d. Exterior of a dorsal valve from Locality 72, Lower Cambrian limestone 5 miles west of Albany, Rensselaer * 
County, New York, illustrating the character of the outer surface. U.S. Nat. Mus. Cat. No. 27334a. 
3e. Cast of the interior of a dorsal valve that is more convex and more oval in outline than the specimen repre- 
sented by figure 3, which is associated on the same hand specimen with it. U.S. Nat. Mus. Cat. 
No. 27333e. 
OBoLus CYANE (Billings) (p. 388). 
Fievre 4. Cast of the interior of a ventral valve, the type specimen, which preserves a portion of the inner layers 
of the shell over the visceral area. 
4a, Imperfect cast of a ventral valve, showing the lamellated shell structure. 
4). Cast of the interior ofa dorsal valve. The muscle scars are obscured in the specimen from which the figure 
has been drawn, and those that appear in the figure are from another specimen occurring in the same 
fragment of limestone. ‘ 
The specimens represented are all from Locality 314d, Lower Ordovician limestone 4 miles northeast of Portland 
Creek. Newfoundland, and are now in the collections of the Geological Survey of Canada. These specimens were 
illustrated by Billings [1865a, figs. 20a-d, p. 215], but further identification of his figures with those in this monograph 
is impossible. 
LINGULELLA IOLE (Billings) (p.:508). 
Ficures 5 and 5a. Ventral and dorsal valves, respectively, from Locality 314d, Lower Ordovician limestone 4 miles 
northeast of Portland Creek, Newfoundland. Geol. Survey Canada. Redrawn from the two speci- 
mens figured by Billings [1865a, figs. 199a-e, p. 215] as Lingula iole. The ventral may be taken as 
the type. 
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