PLATE CIII. 
a’, Anterior adductor impressions. sp. Spondylium. 
a’’, Posterior adductor impressions. s. Median septum. 
r. Diductor scar. vs. Vascular sinus. 
HUENELLA TEXANA (Walcott) (p. 808). 
Ficure 1. Strongly costate ventral valve, the type specimen. U.S. Nat. Mus. Cat. No. 52494a. 
la. Ventral valve with well-defined costz in the mesial sinus, and nearly smooth cardinal slopes. U.S. Nat. 
Mus. Cat. No. 52494b. 
1b. Ventral valve in which there are only slight traces of the radiating costee in the mesial sinus. U.S. Nat. 
Mus. Cat. No. 52494c. 
le. Ventral valve without radiating coste, with back outline. U.S. Nat. Mus. Cat. No. 52494d. 
1d. Ventral valve, with side outline, from Locality 71, Upper Cambrian limestone in Cold Creek Canyon, 
Burnet County, Texas. U.S. Nat. Mus. Cat. No. 52495a. 
le. Dorsal valve, with strong costee on the median fold and cardinal slopes. U.S. Nat. Mus. Cat. No. 52494e. 
1f. Dorsal valve, with fine radiating coste. U.S. Nat. Mus. Cat. No. 52494f. 
lg. Dorsal valve, having median fold with well-marked costs and smooth cardinal slopes, with back outline 
of the same. U.S. Nat. Mus. Cat. No. 52494¢. 
lh. Oblique section of spondylium of ventral valve a short distance from the apex. U.S. Nat. Mus. Cat. 
No. 52494h. 
li. Section of dorsal valve cutting across the spondylinm. U.S. Nat. Mus. Cat. No. 524941. 
With the exception of figure 1d, all the specimens represented are from Locality 68, Upper Cambrian limestone, 
in Packsaddle Mountain, Llano County, Texas. 
HuENELLA aBnormis (Walcott) (p. 805). 
[Text fig. 13, p. 299.] A 
Fiaure 2. Ventral valve with strong radiating coste. U.S. Nat. Mus. Cat. No. 52462a. 
2a and 2a’. Exterior and side views of ventral valve, the type specimen, with radiating cost in the mesial 
sinus. U.S. Nat. Mus. Cat. No. 52462b. 
2b. Cast of interior of ventral valve, showing cast of spondylium, main vascular canals, and muscle scars. 
U.S. Nat. Mus. Cat. No. 52462c. 
2c. Dorsal valve with prominent median fold, from Locality 158, Upper Cambrian limestone north of East 
Gallatin River, near Hillsdale, Threeforks quadrangle (U. 8. Geol. Survey), Gallatin County, Mon- 
tana. U.S. Nat. Mus. Cat. No. 52461a. 
2d and 2d’. Top and side view of nearly smooth dorsal valve. U.S. Nat. Mus. Cat. No. 52462d. 
2e. Dorsal valve with several plications on median fold. U.S. Nat. Mus. Cat. No. 52462e. 
2f. Interior of dorsal valve showing muscle scars and vascular markings. U.S. Nat. Mus. Cat. No. 52462f. 
2e. Posterior view of a ventral valve showing area. U.S. Nat. Mus. Cat. No. 52462g. 
2h. Partial cast of interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52462h. 
2i. Interior of a dorsal valve in which the muscle scars and spondylium (cruralium) have been more or less 
eroded. U.S. Nat. Mus. Cat. No. 524621. 
2}. Cast of the interior of a dorsal valve, showing strong muscle scars and radiating costz on the mesial fold. 
This specimen is associated with the shell represented by figure 2c. U.S. Nat. Mus. Cat. No. 52461b. 
2k. Cast of the interior of a dorsal valve, showing radiating vascular canals at the top of the cast of four strong 
costee. This specimen is associated with the shell represented by figure 2c. U.S. Nat. Mus. Cat. 
No. 52461c. 
21 and 2m. Sections of ventral and dorsal valves cut across the umbo to show sections of the spondylium in 
each valve. U.S. Nat. Mus. Cat. Nos. 52462] and 52462k, respectively. 
With the exception of figures 2c, 2j, and 2k, the specimens represented by figures 2, 2a—m are from Locality 4j, 
Middle Cambrian limestone at the head of Deep Creek, Canyon quadrangle (U. 8. Geol. Survey), Yellowstone 
National Park, Wyoming. 
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