92 PORIFERA. 



and are of two kinds : autodcrmalia in the dermal membrane, and hypodcrmalia 

 beneath the dermal membrane. 



Gastralia are spicules on the gastral membrane or membrane lining the 

 central chamber of the sponge. 



Parenchymalia are spicules in the parenchyma. 



Dictyonalia are the parenchymalia which become fused to form the con- 

 tinuous skeletal framework of the Didyonina. 



Synapticula are bridges of silica connecting neighbouring spicules. 



Oxyhexacts, hexacts with axes running to a point. 



Discohexacts, hexacts with axes enlarged at the extremity. 



Hexasters, hexacts with axes branching into rays at their extremity. 



Pinulus, a pentact or hexact in which one ray bears oblique lateral teeth 

 or prickles (Fig. 78, 1). 



Amphidiscs, a diact at each end of which a convex expansion occurs, which 

 bears six or more backwardly bent marginal teeth (Fig. 78, 9). 



Uncinate, a straight rod, pointed at both ends and beset all over with barbs 

 pointing in the same direction. 



Clavula, a rod which bears at one end a club-shaped or transverse cliscoidal 

 expansion. 



Scopula, a rod which bears at one end a number of rays. 



Sub-order 1. LYSSACINA. 



Hexactinellida in which the spicules either remain altogether isolated, or are 

 in part subsequently and irregularly united by silicious matter or transverse 

 synapticula. 



Tribe 1. HEXASTEROPHORA. Hexasters always present in the parenchyma. 

 The ciliated chambers are sharply separated from one another, and thimble- 

 shaped. 



Fam. 1. Euplectellidae. Dermal skeleton contains sword-shaped oxyhexacts 

 with long proximal ray. Euplcctclla Owen ; Regadrella 0. S. ; Holascus F. E. S. ; 

 Malacosaceus F. E. S. ; Tceycria F. E. S. ; IValtcria F. E. S. ; Habrodictyum 

 W. Th. ; Eudictyum Marshall ; Dictyocalyx F. E. S. ; Rhabdodictyum 0. S. ; 

 Rhabdopectclla 0. S. ; Hertwigia 0. S. ; Hyalostylus F. E. S. 



Fam. 2. Asconematidse. The dermal and gastral skeletons contain pentact 

 or hexact pimili. The hypodermalia and hypogastralia are pentacts with 

 parenchymal discohexasters. Asconema S. Kent ; A ulascus F. E. S. ; Sympagclla 

 0. S.; Polyrhabdus F. E. S.; Balanites F. E. S.; Caulophacus F. E. S.; 

 Trachycaulus F. E. S. 



Fam. 3. Rossellidae. Dermalia always without a distal radial ray. Lanu- 

 ginella O. S. ; Polylophus F. E. S. ; Rossclla Carter; Acanthascus F. E. S. ; 

 Bathydorus F. E. S. ; Rhabdocalyptus F. E. S. ; Crate romorpha Gray ; Aulochone 

 F. E. S. ; Caulocalyx F. E. S.; Aulocalyx F. E. S.; Euryplegma F. E. S. 



Tribe 2. AMPHIDISCOPHORA. Ampliidiscs always present in limiting 

 membranes. Parenchyma without hexasters. Anchoring basalia always present. 

 Chambers not thimble-shaped nor sharply marked off from one another, but 

 forming irregular diverticula of the membrana reticularis. 



Fam. 1. Hyalonematidae. Both dermal and gastral membranes contain 

 numerous pentact pinuli. Hyaloncma Gray ; Pheroncma Leicly ; Poliopoyon 

 Wy. Th. ; Semperellu Gray. 



