PLATE LXXIX. 
a. Central lateral space of area. j. Anterior lateral muscle scar. 
a’. Outer lateral space of area. s. Median septum or ridge. 
el. Cardinal scar. y. Visceral area. 
f. Flexure line of area. vs. Main vascular sinus. 
fa. False area. x. Foraminal aperture. 
h. Central muscle sear. x’’. Cast of apical callosity. 
LINNARSSONELLA GIrTyYI Walcott (p. 666). 
[Pl. LX XVIII, figs. 5, 5a.] 
Figure 1. Exterior of ventral valve with side view of same, the type specimen. U.S. Nat. Mus. Cat. No. 35287a. 
Ja, la’, and la’’. Exterior, posterior, and side views of ventral valve. The arching of the cardinal line of the 
area is well shown in this shell. U.S. Nat. Mus. Cat. No. 35287q. 
1b and 1b’. Exterior, side, and posterior views of ventral valve. The straight, horizontal cardinal line of the 
area is a feature of this shell. U.S. Nat. Mus. Cat. No. 35287b. 
1c and 1c’. Exterior, with side and posterior views, of ventral valve with nearly straight cardinal line of shell 
and area. U.S. Nat. Mus. Cat. No. 35287c. Compare the outline and slope of the area in this speci- 
men with that shown in figures 1 and la. 
1d and le. Exterior and side views of two ventral valves. U.S. Nat. Mus. Cat. Nos. 35287d and 35287e, 
respectively. 
1f-1j. Exterior and side views of dorsal valves, to illustrate variation in outline and convexity of valve. U.S. 
Nat. Mus. Cat. Nos. 35287f-j, respectively. 
1k. Cast of interior of ventral valve with side outline. U.S. Nat. Mus. Cat. No. 35287k. 
1k’. Posterior view of specimen represented by figure 1k, showing posterior outline of cardinal scars and the 
vascular canals; also base of cast of foramen. U.S. Nat. Mus. Cat. No. 35287k. 
11. Cast of the interior and side outline of a dorsal valve. This illustrates all that is known of the interior 
of this valve frem the casts. An interior from another locality is shown by figure Ir. U.S. Nat. 
Mus. Cat. No. 35287 1. 
Im-lp. Casts of the interior and side outlines of ventral valves that illustrate the variation in size and position 
of the cardinal scars and vascular canals. U.S. Nat. Mus. Cat. Nos. 35287m-p, respectively. 
The specimens represented by figures 1, la—p are from Locality 88a, Middle Cambrian limestone about 100 feet 
(30.5 m) above the quartzitic sandstone at the base of the Cambrian, in the northern suburbs of Deadwood, Black 
Hills, South Dakota. 
Ficures lq, lq’, and 1q’’. Top, side, and back views of exterior of ventral valve that is more elevated than usual 
and which has a very high false area. U.S. Nat. Mus. Cat. No. 52188a. 
lr. Interior of dorsal valve on which the area is preserved, also the depressions of the cardinal scars and a 
low, broad, median ridge, but no traces of the central or anterior lateral scars. This is the only speci- 
men found showing the interior of the valve, except in the form of casts (fig. 11). U.S. Nat. Mus. 
Cat. No. 52188b. 
The specimens represented by figures 1q and Ir are from Locality 9p, Upper Cambrian, about 160 feet (48.8 m) 
above the porphyry contact in the limestone of the Reagan sandstone, in SE. NE. } sec. 2, T.4.N., R. 13 W., about 
15 miles (24.2 km.) northwest of Fort Sill, Comanche County, Oklahoma. 
LINNARSSONELLA MINUTA (Hall and Whitfield) (p. 667). 
Fiaure 2. Interior of a ventral valve, showing cardinal scars and foramen. U.S. Nat. Mus. Cat. No. 24553a. 
2a and 2a’. Cast of the interior of a ventral valve with side and posterior outlines. U.S. Nat. Mus. Cat. No. 
24553b. 
2b. Cast of the interior of a dorsal valve and side view of same. U.S. Nat. Mus. Cat. No. 24553c. 
The specimens represented are all from Locality 318h, Upper Cambrian sandy shale on Hamburg Ridge, Eureka 
district, Nevada. They all occur on the same hand specimen with the shells represented by Hall and Whitfield [1877, 
Pl. I, figs. 3 and 4], but the latter shells, which include the type, are not figured in this monograph. 
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