118 Prof. W. Thomson on the " Vitreous " S;ponges. 



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) 



VlTEEA. 



The following is an outline of the slight modifications which 

 I would suggest in Dr. Schmidt's arrangement : — 



Class POKIFERA, 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) SiLiCEA, Gray. " Sponges provided 

 with a siliceous or horny skeleton, or with a horny skeleton 

 strengthened with siliceous spicules." 



Order 1. (P. Silicea) Vitrea. 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) Halichondrida. 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) Halichondrina (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 Esperiadae, the sar- 

 code is soft, and the spicules are of two distinct types. Ex. 

 Halichondna^ Spongilla, Esj)eria. 



Suborder 2. (Halichondrida) GUMMININA ( = Gummineas, 

 Oscar Schmidt). Sponge-substance compact; skeleton of 

 fine densely interwoven horny fibres. Siliceous spicules in 

 some of the genera. Ex. Gummincty Corticium. 



