PLATE XXI 
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1—3. Balanus terebratus Darwin. 
Fig. 1. Labrum, with left-hand palpus; magnified 144 diameters. 
Fig. Maxilla; magnified 144 diameters. 
Fig. 3. Outer maxillae; magnified 144 diameters. 
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ig. 4—14. Balanus arcuatus n. sp. 
Fig. 4. Animal seen from above; magnified 10 diameters. 
Fig. 5. Carino-lateral and lateral compartments, internal view; magnified 15 diameters. 
Fig. 6. a@ and 6, scutum and tergum, internal view; magnified 10 diameters. 
c¢ and d, scutum and tergum, external view; magnified 10 diameters. 
Transverse sections through compartments: a, not far from the orifice, 6, halfway the 
height, c, near the basis; magnified 10 diameters. 
8. Labrum, with left-hand palpus; magnified 144 diameters. 
Fig. 9. Mandible; magnified 64 diameters. 
Fig. 10. Maxilla, outer part with spines; magnified 144 diameters. 
Fig. 11. Outer maxillae, right-hand outer lobe; magnified 144 diameters. 
Fig. 12. Third cirrus, fifth segment; magnified 206,5 diameters. 
Fig. 13. Fourth cirrus, fourth segment; magnified 206,5 diameters. 
Fig. 14. Sixth cirrus, tenth segment; magnified 206,5 diameters. 
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15—20. Balanus quadrivittatus Darwin. 
Fig. 15. Shell seen from above; magnified 7,6 diameters. 
Fig. 16. a@ and 6, scutum and tergum, internal view; magnified 7,6 diameters. 
c¢ and d, scutum and tergum, external view; magnified 7,6 diameters. 
17. Labrum; magnified 64 diameters. 
18. Mandible; magnified 64 diameters. 
19. Maxilla; magnified 64 diameters. 
1g. Maxilla, edge with spines; magnified 206,5 diameters. 
20. Outer maxillae; magnified 64 diameters. 
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