PLATE 16. 



Fig. 18. — M. tehuelcltd. A few zoceeia showing the adult condition with 

 reduced aperture (op.), cak-itied margins, and calcareous tubercles or spines 

 (si).). X 30. 



Fig. 19. — Mcmhranipora membranacea Linnauis. A few zooecia showing 

 membranous aperture and distal spines. X 30. 



Fig. 19a. — M. membranacea. Outline of the operculum. X 70. 



Fig. 20. — il. membranacea. Portion of a zoarium. 



Fig. 21. — Membranipora serrata Hincks. A few zooecia showing ser- 

 rated margin with proximal denticle (d.), spines and membranous aperture. 

 X 30. 



Fig. 21a. — M. serrata. Outline of operculum. X 70. 



Fig. 22. — Membranipora viUosa Hincks. A few zooecia showing adult 

 condition, with flaring spines (fl.sp.), lateral spines (lat.sp.), and minute 

 frontal spines (fr. sp.) ; also tall spine (t. sp.) or process growing in place 

 of a zocecium. X 30. 



Fig. 22a. — M. viUosa. Outline of operculum when closed, with the most 

 anterior pair of frontal spinules. X 70. 



Fig. 22b. — M. viUosa. Outline of operculum partly opened showing 

 broad base for the attachment of muscles (mus.att.). X 70. 



Fig. 23. — M. viUosa. A young colony of seven zooecia showing (a) and 

 (&) the first two zooecia formed, and (c) the third zocecium; also showing 

 the branched spines (br.sp.) characteristic of the youthful stage. X 30. 



[3281 



