10 THE VOYAGE OF H.M.S. CHALLENGER. 



These siliceous spicules which are united iuto a continuous network, or which form, iu 

 virtue of their large size and mutual apposition, a supporting framework for the entire 

 sponge body, were termed by Carter " skeleton spicules," — in opposition to the far smaller 

 " flesh spicules " which are loosely embedded in the soft tissue. In the new genera 

 RosseUa, Carter, and Crateromoiyha, Gray, Carter was able to distinguish several species. 



In 1875 Marshall published his researches on the skeleton of several sponge forms, 

 some imperfectly known, and others newly discovered, e.g., the genera Sclerothamnus, 

 Marshall, and Pervphragella, Marshall. The affinities of the Hexactinellida were 

 discussed by Marshall in a special work. To start with, he distinguished Synauloidse 

 and Asynauloidge. In the former the entire lattice network is said to be penetrated by 

 a continuous system of axial canals, while in the latter the canals of the spicules which 

 fuse to form the network do not communicate. To the Synauloidas Marshall referred 

 only the genus Sclerothamnus. The Asynauloidse he divided into (1) Monacid*, with 

 only one form of spicule ; (2) Pleionacidfe with forks and rosettes, in addition to 

 the six-rayed forms ; and (3) Pollacida3, with numerous distinct forms of spicules, a 

 special dermal skeleton, and an inner covering for the gastral cavities. While Marshall 

 placed in the division Monacidfe only the genus Eurete, he assigned to the Pleionacidse 

 the genera Lanuglnella, Schmidt, Asconema, Kent, Farrea, Bowerbauk, Periphragella, 

 Marshall, Aulodictyon, Kent, Fieldingia, Kent, and A2)hrocaUistes, Gray ; to the 

 PoUacidse, on the other hand, he ascribed the family of the Holteuiadge with Holtenia, 

 Wyv. Thomson, Crateromorpha, Gray, RosseUa, Carter, Sympagella, Schmidt, Placo- 

 dictyum, Schmidt, the family of the Euplectellidse with Euplectella, Owen, and Hahro- 

 dictymn, AV. Thomson, and the family of the Hyalonematidse, with Labaria, Gray, 

 Pheronema, Leidy, Semperella, Gray, and Hyalonema, Gray. 



In 1877, SoUas^ described with great thoroughness a new fossil Hexactinellid genus 

 with two species. Both in the dermal layer, or "oscular plate" as he termed it, and 

 in the thick body mass, SoUas noted a framework of siliceous strands intersecting at 

 right angles. The usual axial canals were present, but the nodes were not penetrated 

 by them, i.e., they did not exhibit any octahedral or lantern-like form. To indicate 

 the systematic position of this new genus, SoUas elaborated the following classification 

 of the Vitreohexactinellids, according to the characters of the skeletal network : — 



I. Sexradiate skeleton spicules, always rectangular. Stauronemata. 



(a) Skeletal network, with simple nodes. 



1. One layer in thickness, . . . Farrea. 



2. Several layers thick, . . . Stauronema. 



(b) Skeletal network having the nodes complicated by 



the presence of an octahedral lantern about 



each node, ..... VentriculitidEe, including Myliusia 



grayi. 

 ' Ann. and Mag. Nat. Hist., ser. 2, vol. xix. p. 1. 



