DESCRIPTION OF PLATES. 



Plates 17, 18, 19, and 20 refer to Clathrozoon wilsoni. 



PLATE 17. 



Figure 1. The skeleton of a dried specimen of Clathrozoon wilsoni, life size, 

 from a photograph. 



Figure 2. Skeleton of part of a colony of Clathrozoon wilsoni, drawn from a 



spirit specimen. 



PLATE 18. 



Figure 3. Restoration of the soft parts. The hard skeleton parts are entirely 

 omitted. Only the end of one of the branches of a colony is represented, hut this 

 is typical of the structure of the whole. The upper surface of the branch is 

 supposed to be cut away to show the connection of the gastrozooids with the 

 ccenosarcal tubes. The outermost of the latter are studded with the defensive zooids. 

 The whole is much magnified, the actual size of the branches being represented in 

 figures 1 and 2. 



Figure 4. Represents a longitudinal section of a small portion of a branch to 

 show the connection of a polype (retracted) with the ccenosarcal tubes. In the 

 figure the polype is connected with three of these. (A) The perisarc walls are shown, 

 and the thin external layer forming at the mouth of the hydrotheca an operculum 

 P. Outline drawn with the camera under Zeiss A. oc. 2. 



Figure 5. Transverse section of a small portion of the outermost part of a 

 branch to show a defensive polype, connected with one of the outer crenosarcal tubes, 

 which is connected again with a deeper lying one. The defensive polype is enclosed 

 by the nematophore. E. is one of the most external tubes, the outer wall of which is 

 formed of the thin layer (P.) of perisarc, on which lies an accumulation of foreign 

 substances, spicules, &c. Outline drawn with camera under Zeiss A. oc 2. 



PLATE 19. 



Figure 11. A small branch much enlarged showing the skeleton only, the soft 

 parts having been dissolved in potash. The hydrothecae are shown arranged spirally 

 and projecting with circular margins slightly from the surface. The network of 

 chitinous tubes is seen to represent somewhat in appearance the clathrate horny 

 skeleton of certain sponges. The somewhat prominent lines on the surface corres- 



