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EXPLANATION OF PLATES. 
[Pls. LVI-LVX, from photographs; Pl. LXVI, from drawings.] 
PiatE LVI. 
1. Poterion atlantica. Vertical section, including cortex of outer surface and adjacent choano- 
some. X 21. 
2. Clionacelata. Section through oyster shell showing included sponge trabecule extending up 
beyond the surface in shape of oscular papilla, which is cut tangentially.  X 15. 
3. Spirastrella andrewsii. Section vertical to the cloacal surface between oscula. % ts. 
4. Cliona celata. Pore papilla. Expanded cap is shown cut in vertical section. The section, 
below, is tangential and shows the surface of the wall of papilla. > 4o. 
5. Clionacelata. Onoyster shells. 1. 
6. Spirastrella andrewsii. Side view of piece shown in fig. 7b. The dermal surface is at top of 
figure. Large incurrent canals, between which lie comparatively thin septa of sponge tissue, 
extend radially inward from dermal surface. 1. 
7a. Spirastrella andrewsii. Small part of cloacal surface. Oscula contracted. 1. 
7b. Spirastrella andrewsii. Small part of outer surface showing incurrent apertures. » 1, 
Pirate LVII. 
8. Suberites undulatus. Whole sponge, from the side. Base of sponge, to the left in the figure. 
Dan 
9. Suberites undulatus. From a section showing fibrous skeleton of the interior. ro. 
to. Suberites undulatus. Entire transverse section through a lobe. The dark patches in the 
choanosome represent the longitudinal skeletal fibers cut across. Io. 
11. Suberites undulatus. From a transverse section through a lobe. Surface of sponge, above and 
to the left. X 15. 
12. Reniera tubifera. Dermal surface of an oscular tube.  2r. 
Pirate LVIII. 
13. Stylotella heliophila. Whole sponge.  X 1. 
14. Tetilla laminaris. Side view of a small specimen. X %. 
15. Reniera tubifera. Whole sponge. 34. 
PuateE LIX. 
16. Reniera tubifera. Longitudinal section through a branch, including both surfaces. 21. 
17. Tetilla laminaris. From a section vertical to one of the flat surfaces of the sponge. The long 
fiber in the interior ascends toward the upper edge of the sponge. 1s. 
18. Stylotella heliophila. Dermal membrane, in surface view. 15. 
19. Stylotella heliophila. Section vertical to surface.  2r. 
PLATE LX. 
20. Esperiopsis obliqua. Biseriate habitus. 14. 
21. Esperiopsis obliqua. Chaliniform habitus. Part of a macerated specimen, including the 
base. X %. 
22. Esperiopsis obliqua. From a longitudinal section through a branch of the macerated specimen 
shown in Fig. 21. X 21. 
23. Esperiopsis obliqua. From a transverse section through a branch of the macerated specimen 
shown in Fig. 21. X 21. 
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