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. Chondrilla). =gl. st, Vosmaer. 
3. Spheraster. 
The rays coalesce to form a solid ball (e.g. Geodia).=gl, Vosmaer. 
B. Irregularia. 
The centre extends to form a line which may be curved, circular, 
ring-shaped, or spiral. 
4. Spiraster. 
A stout spiral with thick spines attached (e.g. Raphyrus). = sé’, 
Vosmaer. When spines terminal, Amphiaster. 
5. Corona. 
A spined ring (e.g. Suberocorona) (°). 
6. Spirula. 
A spiral without spines ia 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. I: Uruguaga). = tr’, 
Vosmaer. 
2. Owystrongylus. 
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. Tylotus. 
A cylindrical rod with a knob at each end (e. g. Crella). = tr™, 
Vosmaer. 
5. Tylostylus. 
A cylindrical rod more or less pointed at one end and knobbed at 
the other (e. g. Suberites). = tr° ac, Vosmaer. Without knob, Stylus. 
Proc. Zoou. Soc.—1886, No. XXXVII. 37 
