118 Prof. W. Thomson on the “ Vitreous” Sponges. 
I believe we are now in a position to define another order, 
equal in value to the CorTicaTa and the HALICHONDRIDA ; 
and for this new order I would propose the term (Porifera) 
VITREA. 
The following is an outline of the slight modifications which 
I would suggest in Dr. Schmidt’s arrangement :— 
Class PORIFERA, Grant. 
Subclass I. (Porifera) CALCAREA, Bowerbank. ‘“‘ Skeleton 
composed of calcareous spicules which are generally three- 
rayed stellate” (Gray), equivalent to Dr. Schmidt’s first 
family. Ex. Grantia, Sycon. 
Subclass II. (Porifera) Stticea, Gray. ‘‘ Sponges provided 
with a siliceous or horny skeleton, or with a horny skeleton 
strengthened with siliceous spicules.” 
Order 1. (P. Silicea) VirrEA. Sarcode in small quantity, 
very soft ; never containing formed horny matter, either fibrous, 
membranous, or granular. The skeleton consists entirely of 
siliceous spicules, either separate (in fascicles or scattered) or 
anastomosing and combined into a continuous siliceous net- 
work. ‘The sarcode contains small spicules of a different cha- 
racter from the general spicules of the skeleton, and of com- 
plicated forms. The spicules, whether of the skeleton or of 
the sarcode, may all be referred to the hexradiate stellate type. 
Ex. Hyalonema, Dactylocalyx. 
Order 2. (P. Silicea) HaticHonpripa. Tuberous, branch- 
ing, cup-shaped, irregular, or incrusting; without any definite 
external cortical layer. The sarcode is abundant, consistent, 
and in all cases is supported by a greater or less amount of 
formed horny matter, which is fibrous, granular and diffused, 
or in the form of more or less distinct membranous expansions. 
The sponge usually contains an abundance of siliceous spicules 
variously arranged. | 
Suborder 1. (Halichondrida) HaticHonpRINna (Lieberkiihn). 
Sarcode abundant, usually consistent. The horny matter 
granular or membranous, but never in the form of a network 
of solid horny fibres. Skeleton consisting mainly of siliceous 
spicules, which are usually essentially of the same form in all 
parts of the sponge. In one family, the Esperiade, the sar- 
code is soft, and the spicules are of two distinct types. Ex. 
Halichondria, Spongitla, Esperia, 
Suborder 2. (Halichondrida) GumMMrinina (= Gumminee, 
Oscar Schmidt). Sponge-substance compact; skeleton of 
fine densely interwoven-horny fibres. Siliceous spicules in 
some of the genera. Ex. Gummina, Corticium. 
