OF THE SPONGIADiE. 277 



296. Represents a small portion of the inner surface of the 

 derpial membrane of Hymedesmia Zetlandica, 

 Bpwerbank, showing the fasciculation of the simple 

 bihamate spicula, the equi-anchorate ones dispersed 

 singly on the membrane and tlie l^rge attenuato- 

 acu^te entirely spined defensive ones in situ. X 308 

 linear. Pages 44 and 190. 



?97. A circular group of inequi-anchorate spicula, situated 

 on one of the interstitial membranes of Hymenia- 

 cidon lingua,, Bowerbank. X 308 linear. See 

 also Figs. 138, 147, &c., Plate VI. Page 49. 



298. A small portion of the dermal membrane |rpm Bic- 



tyocylindrus stuposus, Bowerbank, exhibiting the 

 number ajid position of the minute sphero-gtellate 

 defensive spicula with which it is armed. X 308 

 linear. Page 109. 



INTERMARGINAL CAVITIES. 



299. A section at right angles to the surface of a branch 



of Isodidya simulans, Bowerbank, ejfhibiting the 

 form and position of the intermarginal cavities. 

 X 108 linear. Page 101. 



300. A section oiHalinchondriapanicea, Jqhnston, showing 



the intermarginal cavities at a, immediately beneath 

 thedermalsurface. X lOSlinear. Pagpsl00andl95. 



301. View of a small portion of the inner surface of the 



dermal crust of Geodia Bdrretti, Bowerbank, MS., 

 . with two of the valvular membranes of the proxi- 

 mal ends of the intermarginal cavities : — a, valve 

 closed ; b, a valve partly qpen ; c, c, the radii of 

 the patento-ternate spicula, imbedded in the tis- 

 sues, and forming the areas for the support of the 

 valvular terminations of the intermarginal cavities. 

 X 50 linear. — Longitadinal sections qf two of the 

 intermarginal cavities are shown at a, a, Fig. 354. 

 Plate XVIII. 



Dermal membrane and inhalent pores, pages 

 111 and 173. 



