712 
DE, WYVILLE THOMSON ON HOLTENIA. 
skeleton or of the sarcode, may be referred to the hexradiate type. Examples : Holtenia , 
Hyalonema, Dactylocalyx. 
Order II. (P. Silicea) Radiantia, Wyville Thomson (=Corticata, Oscar Schmidt, in 
part.) Globular, tuberous, or branched sponges, supported by regular radiating sheaves 
of long siliceous spicules, and invested with a more or less dense cortical layer, often 
containing spicules of special and characteristic forms. 
Suborder I. (Radiantia) Corticata (=Corticata, Oscar Schmidt). Cortical layer 
dense and well defined. Examples : Tethya , Geodia, Placospongici. 
Suborder II. (Radiantia) Leptophlea (Wyville Thomson). Cortical layer consisting 
of a thin, almost membranous, sheet of soft sarcode. Examples : Tisiphonia, n. g., 
Stylocordyla, n. g. 
Order III. (P. Silicea) Halichondrida. Sponges tuberous, branching, cup-shaped, 
irregular, or incrusting ; without any definite cortical layer. The sarcode is abundant, 
consistent, and in all cases is supported by a considerable amount of horny matter, which 
is fibrous, granular, and diffused, or in the form of more or less distinct membranous 
expansions. The sponge frequently contains an abundance of siliceous spicules variously 
arranged. 
Suborder I. (Halichondrida) Halichondrina (Lieberkvihn). Sarcode abundant, usually 
consistent. The horny matter is granular or membranous, but is never in the form of a 
network of solid horny fibres. The skeleton consists mainly of siliceous spicules, which 
are usually essentially of the same form in all parts of the sponge. In one family, the 
Esperlacue, the sarcode is soft, and the spicules are of two distinct types. Examples : 
Halichondria, Spongilla, Esperia. 
Suborder II. (Halichondrida) Gummtnina (=Gummine 0 e, Oscar Schmidt). Sponge- 
substance compact ; skeleton of fine densely interwoven horny fibres. Siliceous spicules 
in some of the genera. Examples : Gummina , Corticium. 
Suborder III. (Halichondrida) Spongina (Lieberkuhn). Skeleton an elastic wide- 
meshed network of anastomosing horny fibres, frequently containing foreign bodies, such 
as grains of sand and spicules of other sponges, and occasionally having siliceous spicules 
developed within them, but never associated with free siliceous spicules in the sponge- 
mass. Examples : Spongia, Chalina, Dysidea. 
Order IV. (P. Silicea) Arenosa (=Arenospongia, Gray). — “ Sponge consisting of a 
disk of agglutinated sand, with a series of diverging spicules on the circumference of the 
disk, and with a pencil of similar spicules at the mouth of the oscules on the upper 
surface of the disk” (Gray, Proc. Zool. Soc. May 9th, 1867). Example: Xenospongia. 
Order Y. (P. Silicea) Halisarcina (Lieberkuhn). Sponge destitute of either siliceous 
or horny support. Example : Halisarca. 
The following genera and species may, I believe, be referred with certainty to the 
Order Porifera Yitrea: — 
