DESCRIPTION OF GENERA AND SPECIES. 



Order HEXACTINELLIDA, 0. Schmidt, sen TRIAXONIA. 



Sponges with very loose soft tissue, in which the spicules are either isolated or united 

 by a siliceous cement into a connected sUiceous skeleton. The spicules belong to the 

 triaxial type, or are readily derivable from it. 



Suborder I. LYSSACINA, Zittel (Pis. I.-LXX.; PI. GIL). 



Hexactinellida in which the needles either remain always isolated, or are partly 

 subsequently united in an irregular fashion, often forming strands bound together by 

 sUiceous cement, or ladder-like trabeculae, by means of numerous synapticula. 



Tribe I. HEXASTEEOPHOEA, F. E. Schulze (Pis. I.-XXVL; Pis. LIII.-LXX.; PI. GIL). 



Hexasters are always found iu the parenchyma. The chambers are clearly marked 

 off from one another, and are thimble-shaped. 



Family I. Euplectellid^, Gray (Pis. I.-XX. ; PI. LXX.). 



Saccular or tubular Lyssacina, in which the inferior blind extremity is either rooted 

 in the mud by means of a tuft of fibres, or fixed by a compact base on a firm sub- 

 stratum. The relatively thin lateral wall is in some genera perforated by round or 

 irregular apertures or gaps, more or less regularly arranged, while in others it is non- 

 perforated. The transversely truncated or dome-like upper end is generally (everywhere V) 

 covered by a perforated sieve-plate, and is bordered by a wreath of freely projecting 

 marginal spicules (marginalia), or by a cufi"-like fringe. ■ The outer surface of the lateral 

 wall — apart from the gaps — is either uniformly smooth, or exhibits ridge-like elevations ; 

 sometimes it is richly furnished with radially projecting spicules. On the inner surface 

 there may be observed — apart again from the gaps — furrow-like grooves in more or less 

 regular arrangement. 



The parts of the skeleton are either entirely isolated, or partly united in an irregular 



