18G7.] DR. J. E. GRAY ON SPONGES. 503 



Fain. 2. Aphrocallistid.e. Sponge tubular; tubes reticulate, sub- 

 circular, closed at the end with a netted lid. 



Order II. KERATOSPONGIA. Sponge elastic. Skeleton formed 

 of horny netted fibres, generally without, but sometimes more 

 or less strengthened Avith, minute siliceous spicules or grains of 

 sand. 



Fam. 3. Spongiad^. Skeleton formed of one kind of reticulated 

 horny fibres, not enclosing any spicules or sand. 



Fam. 4. Hirciniad.^. Skeleton formed of two kinds of horny 

 fibres : — the one, forming the base of the skeleton, thick, reticu- 

 lated, with a more or less distinct central line of minute spicules 

 or grains of sand ; the other very slender, at the apex of the 

 branches, which do not anastomose. 



Fam. 5. Dysideid^e. Skeleton formed of reticulated horny fibres 

 with sand or spicules of other sponges imbedded in the centre, 

 and covered with a more or less thick coat of horn}'^ matter. 

 Brittle when dry. 



Fam. 6. ChalinidvE. Skeleton formed of reticulated horny ana- 

 stomosing filaments^ which have one or more series of siliceous 

 spicules in the central line. 



Fam. 7. Opiustospongiad.^i;. Skeleton netted horny, or expanded 

 skin-like fibres, covered with superficial spicules, forming an 

 irregular coat, or which are single or grouped, and divergent 

 from the surface. 



Fam. 8. Piiakelliad.e. Skeleton formed of closely reticulated 

 horny fibres, forming an expanded mass; spicules numerous, in 

 bundles, forming radiating, repeatedly branched lines, which do 

 not anastomose on the surface. 



Subsection 2. Spicular Sponges (Spicxjlospongi.e). Spoiiffe 

 Jieshy, more or less strengthened by fasciculated or scattered 

 siliceous sjiicides, the bundle being sometimes slightly covered 

 ivith a thin layer of horny matter. The sarcode is generally 

 abundant ; in some few, as Euplcctella, it is thin, mucilaginous, 

 and deciduous. 



Order III. LEIOSPONGIA. Sponge-spicules only of one kind, 

 often varying in size and shape in the same species. 



Fam. 9. Halichondriad-e. Skeleton composed of fusiform or 

 pin-shaped spicules variously fasciculated together, or rarely 

 united by a small quantity of horny matter. Sarcode granular 

 or fleshy. 



Fam. 10. PoLYMASTiAD.E. Sponge with tubular fistulous branches; 

 tubes open at the end, and formed of longitudinal and trans- 

 verse fascicules of fibres. 



