1886.] POSITION AND CLASSIFICATION OF SPONGES. 561 



The following six forms can be distinguished : — 



A. Regularia, 

 The rays radiating from one point. 



1 . Oxyaster. 



With long, slender, pointed rays (e. g. Stelletta). = st, Vosmaer. 



2. Euaster. 



With stout, pointed, conic rays (e. g. Chondrilld).=gl. st, Vosmaer. 



3. Spheraster. 



The rays coalesce to form a solid ball {e.g. Geoclia).=gl, Vosmaer. 



B. Irregularia. 



The centre extends to form a line which may be curved, circular, 

 ring-shaped, or spiral. 



4. Spir aster. 



A stout spiral with thick spines attached (e. g. Raphyrus). ^ st^, 

 Vosmaer. When spines terminal, Amphiaster, 



5. Corona. 



A spined ring (e. g. Suherocorona) (?). 



6. Spirula. 



A spiral without spines {e.g. Spiretta). 



These anaxon spicules never form part of the supporting skeleton, 

 but are invariably flesh-spicules (Microsclera). 



2. Monaxonia. 



With one straight or curved axis, sometimes with lamellar out- 

 growths. 



A. Supporting Spicules (Megasclera). 



1. Strongylus. 



A cylindrical rod rounded at each end {e.g. Vruguaga). = tr^, 

 Vosmaer. 



2. Oxystrongylus. 



A cylindrical rod abruptly pointed at each end {e.g. Pachychalina). 



3. Oxyus. 



A gradually pointed, spindle-shaped spicule {e. g. Spongilla). 

 = ac, ac, and ac^, Vosmaer. Diact, F. E. Schulze. 



4. Ty lotus. 



A cylindrical rod with a knob at each end {e. g. Crella). = /r", 

 Vosmaer. 



5. Tylostylus. 



A cylindrical rod more or less pointed at one end and knobbed at 

 the other {e. g, Suherites). = tr" ac, Vosmaer. "Without knob, Stylus. 

 Proc. Zool. Soc— 1886, No. XXXVII. 37 



