284 ANATOMY AND PHYSIOLOGY 



Order 2. — Silicea. 



Sub-order I. 

 Pig. 



353. Pachymatisma Johnstonia, Bowerbanh. A section 



at right angles to the surface, exhibiting the irregu- 

 larity of the interstitial structures directly beneath 

 the dermal crust. ' X 50 linear. Page 172. 



354. GeodixBakkwuti, Bowerbank.MS. A section at right 



angles to the surface, exhibiting the radial disposi- 

 tion of the fasciculi of the skeleton, and a portion 

 of the dermal crust of" the sponge. X 50 linear. 

 — a, intermarginal cavities ; S^, the basal dia- 

 phragms of the intermarginal cavities ; c, imbedded 

 ovaria forming the dermal crust of the sponge ; d, 

 the large paten to-tern ate spicula, the heads of 

 which form the areas for the valvular bases of the 

 intermarginal cavities ; e, recurvo-ternate defensive 

 and aggressive spicula within the summits of the 

 great intercellular spaces of the sponge ; /, portions 

 of the interstitial membranes of the sponge, crowded 

 with minute stellate spicula; </j portions of the 

 secondary system of external defensive spicula. 

 Pages 122, 169 and 171. 



355. EcioNEMiA ACERvus, Bowerbouk, AJS. A section at 



right angles to the surface, exhibiting the radial 

 fasciculi of the peripheral system, with the ternate 

 apices of the spicula directly beneath the dermal 

 membrane. X 50 linear. Page 174. 



356. Alcyoncellum aspergillum, Quoi/ et Gaimard 



(Euplectella — Owen). A portion of the surface of 

 the sponge, with its great inhalent areas ; a, the 

 primary longitudinal fasciculi; b, the secondary 

 or transverse fasciculi. X 7 linear. Page 177. 



357. The oscular area of A. aspergillum, with a marginal 



boundary, and the congregated oscula within, 

 natural size. Page 177. 



