PLATE XIV. 
e. Trapezoidal area, including central, middle 1. Outside lateral muscle sear. 
lateral, and outside lateral muscle scars. vs. Main vascular sinus. 
h. Central muscle scar. s. Median septum. 
i. Transmedian muscle sear. x. Heart-shaped cavity. 
j. Anterior lateral muscle sear. 
Oxsotus (ScHMipriA) CELATUS (Volborth) (p. 444). 
Figure 1. Exterior of ventral valve. U.S. Nat. Mus. Cat. No. 35237a. 
la. Interior of ventral valve. U.S. Nat. Mus. Cat. No. 35237b. Specimen figured by Walcott [1898b, PI. 
XXVI, fig. 1] as Obolus (Lingulella) celatus. 
1b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 35237c. 
lc. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 35237d. Specimen figured by Walcott [1898b, Pl. 
XXVI, fig. 2] as Obolus (Lingulella) celatus. 
The specimens represented are all from Locality 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, 
Esthonia, Russia. 
Oso us (SCHMIDTIA) ACUMINATUS Mickwitz (p. 442). 
Figure 2. Exterior of ventral valve. U.S. Nat. Mus. Cat. No. 5153la. 
2a. Interior of ventral valve. U.S. Nat. Mus. Cat. No. 51531b. 
2b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 51531c. 
2c. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 51531d. 
The specimens represented are all from Locality 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, 
Esthonia, Russia. 
Oxo us (Scumiprr1a) opTusus Mickwitz (p. 448). 
Figure 3. Exterior of ventral valve. U.S. Nat. Mus. Cat. No. 51532a. 
3a. Interior of ventral valve. U.S. Nat. Mus. Cat. No. 51532b. 
3b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 51532c. 
3c. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 51532d. 
The specimens represented are all from Locality 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, 
Esthonia, Russia. 
Oxotus (ScumiIptr1A) crassus Mickwitz (p. 446). 
Ficure 4. Exterior of ventral valve. U.S. Nat. Mus. Cat. No. 51530a. 
4a. Interior of ventral valve. U.S. Nat. Mus. Cat. No. 51530b. 
4b. Exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 51530c. 
4c. Interior of dorsal valve. U.S. Nat. Mus. Cat. No. 51530d. 
4d. Interior of an elongate form of a dorsal valve. U.S. Nat. Mus. Cat. No. 51530e. 
The specimens represented are all from Locality 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, 
Esthonia, Russia. 
LINGULELLA (LEPTEMBOLON) LINGULEZFORMIS (Mickwitz) (p. 542). 
Ficure 5. A large dorsal valve from Locality 396a, passage beds between the Upper Cambrian and the Ordovician, 
“slauconite sandstone,’ at Leppiko, near Leetz, Esthonia, Russia. Copied from Mickwitz [1896, 
Pl. III, figs. 17a-b]. 
5a. Small dorsal valve associated with specimen represented by figure 5b. U.S. Nat. Mus. Cat. No. 51537a. 
5b. Small ventral valve from Locality 395, Upper Cambrian Obolus sandstone at Joa, near Jegelecht, Esthonia, 
Russia. The beak of this specimen was broken away and has been restored in outline on the figure. 
U.S. Nat. Mus. Cat. No. 51537b. 
