PLATE XXXI. 
a. Central lateral space of area. i. Transmedian muscle sear. 
a’. Outer lateral space of area. j. Anterior lateral muscle scar. 
ce. Trapezoidal area, including central, middle 1. Outside lateral muscle scar. 
lateral, and outside lateral muscle scars. p. Pedicle groove. 
f. Flexure line of area. v. Visceral cavity. 
h. Central muscle scar. vs. Main vascular sinus. 
LInGULELLA NatTHoRSTI Linnarsson (p. 521). 
Ficure 1. Cast of the interior of ventral valve, from Locality 320x, Lower Cambrian limestone at Andrarum, Province 
of Christianstad, Sweden. U.S. Nat. Mus. Cat. No. 18199a. 
la and 1b. Casts of the interior of dorsal valves associated with the specimen represented by figure 1. U.S. 
Nat. Mus. Cat. Nos. 18199b and 18199c, respectively. 
lc. Ventral valve preserving most of the shell, from Locality 8y, Lower Cambrian limestone at Skarésen, 
Dalarne, Sweden. U.S. Nat. Mus. Cat. No. 51739a. ; 
1d and le. Dorsal valves associated with the ventral valve represented by figure lc. U.S. Nat. Mus. Cat. 
Nos. 51739b and 51739c, respectively. 
lf. Ventral valve associated with the ventral valve represented by figure 1c. U.S. Nat. Mus. Cat. No. 51739d. 
1g and 1h. Dorsal valves associated with the ventral valve represented by figure lc. U.S. Nat. Mus. Cat. Nos. 
51739e and 51739f, respectively. 
LINGULELLA SIEMIRADZEIE (Walcott) (p. 531). 
Ficure 2. Ventral valve, the type specimen, showing portion of the outer surface and the finely striated inner layer 
of shell. U.S. Nat. Mus. Cat. No. 35258a. : 
2a. Cast of part of a dorsal valve. U.S. Nat. Mus. Cat. No. 35258b. 
The specimens represented are both from Locality 368, Middle Cambrian quartzitic sandstones in the Pepper Moun- 
tains, near Sandomierz, on the Vistula, Russian Poland. 
LINGULELLA FERRUGINEA Salter (p. 496). 
[Pl. XXIX, figs. 1, la-w, 2, 2a-f; Pl. XXX, fig. 1; and Pl. XXXV, figs. 4, 4a-b.] 
Figure 3. Ventral valve from Locality 310p, Middle Cambrian limestone at Borgholm, Oeland Island, Sweden. 
U.S. Nat. Mus. Cat. No. 51752a. 
3a. Dorsal valve from Locality 310y, Middle Cambrian limestone of Kiviks Esperéd, Province of Malméhus, 
Sweden. U.S. Nat. Mus. Cat. No. 18205a. 5 
3b. Short ventral valve from Locality 310z, Middle Cambrian limestone at Brantevik, Sweden, that is doubt- 
fully referred to this species. U.S. Nat. Mus. Cat. No. 51750a. 
3c. Ventral valve doubtfully referred to the species from Locality 320m, Middle Cambrian at Kinnekulle, 
Province of Skaraborg, Sweden. Copied from Linnarsson’s figure [1876, Pl. IIT, fig. 28] of ‘‘Lingula 
or Lingulella sp.” 
LINGULELLA LEPIS (Salter) (p. 514). 
Freurr 4. Ventral valve from Locality 366k, Upper Cambrian shales, Penmorfa, Merionethshire, North Wales. 
Enlarged drawing of the specimen represented in figure 4a. Copied from Davidson [1871, Pl. XLIX, 
fig. 31a]. 
4a. The ventral valve figured in figure 4, natural size. Copied from Davidson [1871, Pl. XLIX, fig. 31]. 
4b. Cast of the interior of a ventral valve from Locality 8x, passage beds between the Upper Cambrian and the 
Ordovician, at Slemmestad, near Christiania, Norway, showing area, cast of pedicle groove, and 
visceral cavity. U.S. Nat. Mus. Cat. No. 51741a. 
de. Exterior of a strongly convex, highly polished ventral valve associated with the shell represented in figure 
4b. Traces of radiating ribs, so strongly developed in figure 4d, are visible with a strong lens. U.S. 
Nat. Mus. Cat. No. 51741b. 
4d. Dorsal valve associated with the shell represented in figure 4b, marked by strong radiating ribs and fine 
concentric strie. U.S. Nat. Mus. Cat. No. 51741c. 
de. Narrow form of dorsal valve, showing outline of elongate visceral cavity, from Locality 9f, Upper Cambrian 
limestones at Ncersnees, west of Christiania, Norway. U.S. Nat. Mus. Cat. No. 51742a. 
4f. Cast of part of a broad form of a dorsal valve associated with the shell represented by figure 4b. U.S. 
Nat. Mus. Cat. No. 51741d. 
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