PLATE XCV.* 
a’. Anterior adductor scars. ce. Crura. 
a’’. Posterior adductor scars. j. Cardinal process. 
b. Dental sockets. r. Diductor scars. — 
EoortTHiIs CHRISTIANL® (Kjerulf)% (p. 775). 
Fiaure 1. Cast of exterior of ventral valve. U.S. Nat. Mus. Cat. No. 52306h. 
la,-lb, and 1c. Casts of ventral valves showing muscular area. U.S. Nat. Mus. Cat. Nos. 52306a-c, respec- 
tively. 
1d, le, and 1f. Casts of exterior of dorsal valves. U.S. Nat. Mus. Cat. Nos. 52306d-f, respectively. 
lg. Cast of interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52306g. 
The specimens represented by figures 1, la-g are from Locality 310d, Upper Cambrian Ceratopyge slate at Borgholm, 
Oeland Island, Sweden. 
Ficure lh. Dorsal valve with strong median sinus, from Locality 323x, Upper Cambrian Ceratopyge slate at Rus- 
selékken, near Christiania, Norway. U.S. Nat. Mus. Cat. No. 52307a. 
EoorrHis pAuNuS (Walcott) % (p. 776). 
Ficure 2. Ventral valve with side outline from Locality 310j, passage beds between the Upper Cambrian and the 
Ordovician, Ceratopyge limestone at Borgholm, Oeland Island, Sweden. U.S. Nat. Mus. Cat. No. 
52309a. 
2a and 2b. Dorsal valves in limestone matrix of Locality 328z, passage beds between the Upper Cambrian and 
the Ordovician, Ceratopyge limestone at Téien, near Christiania, Norway. U.S. Nat. Mus. Cat. 
Nos. 52308a and 52308b, respectively. Figure 2a represents the type specimen. 
2e. Dorsal valve associated with the specimen represented by figure 2. U.S. Nat. Mus. Cat. No. 52309b. 
EoorTHIs TULLBERGI (Walcott) * (p. 790). . 
Figure 3. Partly exfoliated ventral valve, thetypespecimen, from Locality 390, passage beds between the Upper Cam- 
brian and the Ordovician, at Alunbruk (alum works), Oeland Island, Sweden. U.S. Nat. Mus. Cat. 
No. 58309. 
EoortHis wmant (Walcott)? (p. 791). 
Figure 4. Cast of interior of ventral valve from Locality 8x, passage beds between the Upper Cambrian and the Ordo- 
vician, Ceratopyge limestone at Slemmestad, about 3 miles (4.8 km.) southwest of Christiania, Norway. 
U.S. Nat. Mus. Cat. No. 52311a. 
4a. Cast of interior of dorsal valve, the type specimen’, from Locality 323w, Upper Cambrian black argil- 
laceous shale of “‘Etage 3a” at Christiania, Norway. U.S. Nat. Mus. Cat. No. 52313a. 
4b. Exfoliated dorsal valve from Locality 310j, passage beds between the Upper Cambrian and the Ordovician, 
Ceratopyge limestone at Borgholm, Oeland Island, Sweden. U.S. Nat. Mus. Cat. No. 52312a. 
4c and 4d. Ventral and dorsal valves associated with the specimen represented by figure 4a. U.S. Nat. Mus. 
Cat. Nos. 52313b and 523138c, respectively. 
PROTORTHIS ? HUNNEBERGENSIS Walcott® (p. 740). 
Ficure 5. Cast in shale of exterior of ventral valve. U.S. Nat. Mus. Cat. No. 52428a. 
5a. Cast of compressed ventral valve, the type specimen. U.S. Nat. Mus. Cat. No. 52428b. 
5b. Cast in shale of exterior of dorsal valve. U.S. Nat. Mus. Cat. No. 52428c. 
5c. Partial cast of interior of dorsal valve. U.S. Nat. Mus. Cat. No. 52428d. 
The specimens represented are all from Locality 390%, passage beds between the Upper Cambrian and the Ordo- 
vician, shales at Mossebo, on Hunneberg, Province of Skaraborg, Sweden. 
a A photograph of this plate was sent to Prof. J. C. Moberg, who reproduced it as Plate II of his paper on the Ceratopyge region [Moberg and 
Segerberg, 1906, Pl. II). 
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