SPONGES 153 



number. Body form erect, lamellar, cup-shaped, or branched ; skeleton 

 fibres plumose, often more or less radiate in arrangement. Genera 

 jHymeniacidon, Bwk. [Eoc.] ; Phakellia, Bwk. (Figs. 35, 36) ; Ciocalypta, 

 B\vk. ; Tragosia, Gray ; Syringella, O.S. ; jAxinella, O.S. [Garb. Eoc.] ; 

 Raspailia, Ndo. ; Hiyyinsia, Higgin ( = Dendropsis, R. and D.) ; Thrinaco- 

 phora, R. ; Auletta, O.S. ; Dictyonella, O.S. ; Acanthella, O.S.;. Halicnemia, 

 Bwk. ; Amorphinopsis, Crtr. ; Vosmaeria, Fristedt ; Sollasella, Ldf. ; 

 Trikentrion, Ehlers; Tetranthella, Ldf.; Vibulinus, Gray ( = St elligera, 

 Ldf.) ; Sigmaxinella, D. 



APPENDIX Monaxonida incerti sedis. Genera *Climacospongia, 

 Hinde [Sil.] ; *Lasiocladia, Hiiide [Dev.] ; * Acanthorrhaphis, Hinde 

 [Cret.] ; *Atractosella, Hinde [Sil.] ; *Haplistion, Young [Garb.] ; *Tricho- 

 .ipongia, Bill [Gambr.]. 



GRADE III. KERATOSA. 



Demospongiae in which the skeleton consists of fibres of 

 spongin, without "proper" spicules. 



The Keratosa are divided by Lendenfeld into the two orders Mono- 

 ceratina, including those forms whose nearest affinity is with the Monaxo- 

 nida, and Hexaceratina, supposed to be descended from the Hexactinellida, 

 and including the Aplysillidae and the Halisarcidae (Myxospongida). 



As regards the Hexaceratina so called, the theory of their affinity is 

 based partly upon the resemblance of the (frequently) triaxon horny 

 spicules of one genus (Darwinella) to the triaxon siliceous spicules of 

 Hexactinellids, and partly upon resemblances in their canal systems. 

 Since, however, nothing whatever is known of the origin and formation 

 of either of the two kinds of spicules in question, the assumption of their 

 genetic connection, however enticing as a speculation, is scarcely sufficiently 

 well founded for use as a systematic character ; and the fact that the 

 Aplysillidae and Halisarcidae have thimble-shaped chambers is not con- 

 clusive proof of their affinity either with one another or with the 

 Hexactinellids. 



On the other hand, Lendenfeld's two groups undoubtedly represent a 

 sharp and natural cleavage of the Keratosa, after removal of the Halisar- 

 cidae, and we therefore retain them with an alteration of the names. 

 The one, characterised by a reticulate type of skeleton, we term Dictyo- 

 ceratina ; the other in which the skeleton is dendritic, we term Dendrocer- 

 atina. 



ORDER 1. Dictyoceratina ( = Monoceratina, Ldf.). 



The spongin skeleton has the form of a network (or rather feltwork) of 

 anastomosing fibres. 



FAMILY 1. SPONGIDAE, Gray. Skeletal fibres solid ; ground sub- 

 stance round the chambers granular ; canal system aphodal. Genera 

 Eusponyia, Broiin (Fig. 39) ; Hipposponyia, F.E.S. ; Cacosponyia, O.S. ; 

 Coscinoderma, Grtr. ; Stelospongus, O.S. ; Hircinia, Ndo. ; Phyllospongia, 

 Ehlers ; Carteriosponyia, Hyatt. FAMILY 2. SPOXGELIIDAE, Ldf. Fibres 

 solid, usually with considerable quantities of foreign bodies; ground 



