OF THE SPONGIAD^!, 287 



FIG. 



371. HYMEDESMIA ZETLANDICA, Bowerbank. Exhibiting 



the disjoined fasciculi of the skeleton in situ. 

 X 108 linear. See also Fig. 296, Plate XVIII, 

 Page 190. 



Sub- Order 2. 



372. HYMENIACIDON CARUNCULA. Exhibiting the dispersed 



condition of the skeleton spicula on the interstitial 

 membranes of the sponges. X 108. Page 192. 



Sub- Order 3. 



373. HALICHONDRIA INCRUSTAISS. Exhibiting a better 



type of the skeleton structure of the genus than 

 Halichondria panicea. X 50 linear. See also 

 Figs. 300, 303, Plate XIX, for Halicliondria 

 panicea. Page 195. 



374. HYALONEMA MIRABILIS, Gray. The figure represents 



a portion of the spiral fasciculus of single, elongated 

 and very large spicula, forming the axial skeleton 

 of a columnar cloacal system ; surrounded by a 



i/ ... 



portion of its coriaceous envelop, exhibiting 

 numerous oscula on its surface ; natural size. 

 Copied from the figure in the ' Proceedings of the 

 Zoological Society of London, for 1857.' Pagel97. 



375. A portion of the skeleton of Byalonema wirabilis, 



Gray, showing the indefinite nature of the sepa- 

 rated elongated fasciculi of the skeleton. X 50 

 linear. Page 197. 



) ? >76. ISODICTYA NORMANI. Exhibiting the regular and 

 nearly rectangular structure of the network of the 

 skeleton of spicula. X 108. 

 Spowgilla. Agrees perfectly in the structure of 

 the skeleton with Isodicfya, but is distinguished from 

 that genus by the peculiarities of the reproductive 

 organs. Pages 197 and 199. 



