SPONGES 153 



mimber. Body form erect, lamellar, cuii-sliaped, or Ijranched ; skeleton 

 fibres plumose, often more or l&ss radiate in arrangement. Genera — 

 iHymeiiiacidon, Bwk. [Eoc] ; Phakellia, Bwk. (Figs. 35, 36) ; Ciocal\jj)ta, 

 Bwk. ; Tiaijosia, Gray; Syringella, O.S. ; jAxinella, O.S. [Carb. Eoc.]; 

 Rasjyaib'a, Ndo. ; Hujginsiu, Higgiu { = JJendrojJsis, 11. and D.) ; Thrinaco- 

 2)hora,}i.; Auletta, O.S.; Dictyonella, O.S.; Acanthella, O.S.; Halicnernia, 

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

 Trikentrion, Ehler.s ; Tetranfhella, Ldf.; Vihulinus, Gray { = Stelli(jcra, - 

 Ldf) ; Sigrnaxinella, D. 



Appendix — Monaxonida incerti sedis. Genera — *Cli'niacospon(jia, 

 Hinde [Sik] ; *Lasiocladia, Hinde [Dev.] ; * Acanthorrhuphis, Hinde 

 [Cret.] ; *Atractosella, Hinde [Sil] ; * Hcqilintion, Young [Carb.] ; *Tricho- 

 spongia, Bill [Cambr.]. 



Grade III. Keratosa. 



Demospongiae in whicli the skeleton consists of fibres of 

 .spongin, without " proper " spicules. 



The Kerato.sa are divided by Lendenfeld into the two orders — Mono- 

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

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

 and including the Aj)lysillidae and the Halisarcidae (Myxospongida). 



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

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

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

 Hexactinellids, and partly upon resemblances in their canal system.s. 

 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 .sj'stematic character ; and the fact that the 

 Apbjsillidae and Halisarcidae have thimble-shaped chambere is not con- 

 clusive proof of tlieir affinity either Avith 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 Halimr- 

 ridae, 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 otlier in which the skeleton is dendritic, we term Dcndrocer- 

 atina. 



Ordeh 1. Dictyoceratina (; = Monoceratina, Ldf). 



The sjxjngin skeleton has tlie form of a network (or ratlier feltwork) of 

 mastomosing fibres. 



Family 1. Spoxgidae, Gray. Skeletal filnes solid ; ground sub- 

 stance round the chambei-s granular ; canal .system ai)lHxlal. Genera 



Euspowjia, Bronn (Fig. 39; ; Hippospomjia, F.E.S. ; Cacospontjia, O.S. ; 

 Coscinoderma, Crtr. ; Hteloqjongun, O.S. ; Hircinia, Ndo. ; Phyllospongiuy 

 Elilcrs ; Carteriosponfjia, Hyatt. Family 2. Spoxgeliidae, Ldf Fibres 

 solid, u.sually with consideraJile quantities of foreign bodies; ground 



