A GUIDE TO THE SPONGES 237 



b. Order HEXACERATIDA. Skeleton formed of fibers, or no 

 skeleton. {Darwinella, Aplysilla, Halisarca.) 



. Subclass DEMOSPONGI.(E. Ciliated chambers small ; skeleton 

 formed of spicules of one or four axes; or no skeleton. 



a. Order TETRACTINELLIDA, Skeleton formed of tetraxial meg- 



ascleres, rarely reduced to microscleres, or no skeleton at all. 



(i) Suborder Choristina. Skeleton flexible, without interlocking 

 desmas. 



(i) Family Sigmatophoridae. Megascleres present. Micro- 

 scleres in the form of sigmaspires, or none. {Tetilla, 

 Cinachyra.) 



(ii) Family Astrophoridae. Megascleres present. Microscleres 

 in the form of asters. (Thenea, Stelletta, Disyringa, 

 Geodia. Pachyntalisma } 



(iii) Family Microsclerophoridae. No microscleres. {Plakina, 

 Oscarella, Chondrosa.) 



(2) Suborder Lithistina. Skeleton rigid, formed of interlocking 

 desmas 



(i) Family Triaenidae. Ectosome containing triaenes. {Theonella, 

 Desnianthus, Stphonta, Corallistes, Pleroma,) 



(ii) Family Rhabdosidae. Ectosome containing microstrongyles, 

 free or in desmas. {Neopelta.) 



(iii) Family Anoplidae. Ectosome without spicules. {Azoriea. 



Vetulina.) 



b. Order MONAXONIDA. Skeleton formed of megascleres of only 

 one axis. 



(i) Suborder Hadromerina. Ordinarily with a cortex; mega- 

 scleres in radial bundles; microscleres in asters or absent, 

 never in the form of spires or sigmas. 



(i) Family Aciculidae. Diactinous megascleres. {Tethya, Hemi- 

 asterella, Stylocordyla.) 



(ii) Family Clavulidae. Monactinous megascleres. {Spirastrella, 

 Subentes* Polymastia, Chona.) 



(2) Suborder Halichondrina. Ordinarily no cortex; megascleres 

 entirely oxeas arranged in a network. {Sponeilla*, Chalina*, 

 Renter a, Halichondria, Tedania,Esperella, Cladorhiza, Myxilla, 

 Clathria, Axmella.*) 



c. Order MONOCERATIDA. Skeleton formed of spongin fibers 



with or without microscleres. {Euspongia* Hippospongia* 

 Aplysina* Druinella, Stelospongia* Hircinia* St>ongelia* 

 Phoriospongta.*) 



* Represented in Museum Collection. 



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