PLATE XX. 
h. Central muscle scar. y. Visceral cavity. 
j. Anterior lateral muscle sear. vs. Main vascular sinus. 
s. Median septum. x. Heart-shaped cavity. 
LINGULELLA MANTICULA (White) (p. 517). 
Figure 1. Cast of the interior of a ventral valve from Locality 313f, Upper Cambrian limestone at Schellbourne, 
Schell Creek Range, Nevada. U.S. Nat. Mus. Cat. No. 8569a. 
la. Dorsal valve associated on the same hand specimen with the valve represented by figure 1. U.S. Nat. 
Mus. Cat. No. 8569b. 
lb. Cast showing part of the interior of a more elongate dorsal valve than that represented by figure la, but 
associated on the same hand specimen with it. U.S. Nat. Mus. Cat. No. 8569c. 
1c. Type specimen, the ventral valve, from the locality represented by figures 1, la-b. U.S. Nat. Mus. 
Cat. No. 8569d. When the plates were made up this specimen could not be located and the original 
drawing prepared for White [1877, Pl. III, fig. 2b] was used. The specimen has been found on the 
same hand specimen with the type of Acrotreta pyxidicula. 
OpoLus RoTUNDATUS (Walcott) (p. 411). 
Figure 2. A ventral valve, the type specimen, from Locality 318d, Lower Ordovician limestone near Schellbourne, 
Schell Creek Range, Nevada. U.S. Nat. Mus. Cat. No. 27337a. 
2a. Cast of the interior of a dorsal valve associated with the shell represented by figure 2. U.S. Nat. Mus. 
Cat. No. 27337b. 
2b. Ventral valve from Locality 160a, Upper Cambrian limestone, west of Bear Creek, south of Gallatin 
Valley, Montana. U.S. Nat. Mus. Cat. No. 27338a. 
2c. A small but very perfect ventral valve associated with the valve represented by figure 2b. U.S. Nat. 
Mus. Cat. No. 27338b. 
2d. A small and characteristic dorsal valve associated with the valves represented by figures 2b and 2c. U.S. 
Nat. Mus. Cat. No. 27338c. 
2e. Dorsal valve from Locality 302b, Middle Cambrian limestones near Crowfoot Ridge, Yellowstone National 
Park, Wyoming. U.S. Nat. Mus. Cat. No. 35207a. Specimen figured by Walcott [1899, Pl. LX, 
fig. 2a] as the dorsal valve of Obolus (Lingulella) desideratus. (See description of fig. 4, below.) 
/ 
LINGULELLA POGONIPENSIS (Walcott) (p. 525). 
Ficure 3. Ventral valve, the type specimen, showing cast of the area and the pedicle furrow. U.S. Nat. Mus. 
Cat. No. 27332a. ; 
3a. Small, partly exfoliated ventral valve. U.S. Nat. Mus. Cat. No. 27332b. 
3b. Partly exfoliated dorsal valve. U.S. Nat. Mus. Cat. No. 27332c. 
3c. Partly exfoliated ventral valve. U.S. Nat. Mus. Cat. No. 27332d. 
The specimens represented are all from Locality 201, passage beds between the Upper Cambrian and the 
Ordovician, in the ridge east of Hamburg Ridge, Eureka district, Nevada. 
LINGULELLA DESIDERATA (Walcott) (p. 492). 
Ficure 4. Partly exfoliated ventral valve from Locality 302 1, Upper Cambrian limestone, Gallatin Range, Yellow- 
stone National Park, Wyoming. U.S. Nat. Mus. Cat. No. 33867a. Type specimen, figured by 
Walcott [1899, Pl. LX, fig. 2] as Obolus (Lingulella) desideratus.. (See description of fig. 2e, above.) 
4a. Dorsal valve, associated with the specimen represented by figure 4. U.S. Nat. Mus. Cat. No. 33867b. 
4b and 4c. Ventral and dorsal valves on the same piece of limestone from Locality 61, Upper Cambrian, near 
the Hamburg mine, Eureka district, Nevada. U. S. Nat. Mus. Cat. Nos. 27313a and 27313b, 
respectively. 
5 and 5a. Ventral valves from Locality 94xx, Middle Cambrian shaly limestones at Givens Mill, on Cowan 
Creek, Cherokee County, Alabama. U.S. Nat. Mus. Cat. Nos. 27355a and 27355b, respectively. 
5b. Ventral valve from Locality 930, Upper Cambrian shales near Jordans, on Cowan Creek, Cherokee 
County, Alabama. U.S. Nat. Mus. Cat. No. 56990a. 
5c. Dorsal valve, slightly distorted in outline, from Locality 940, Upper Cambrian shale near Givens Ford, 
on Cowan Creek, Cherokee County, Alabama. U.S. Nat. Mus. Cat. No. 56991a. 
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