146 



SPONGES 



compromise between logical necessities and natural affinities. It is 

 hoped that the classification here adopted represents such a com- 

 promise in which the disturbance of the true relationships is reduced 

 to the unavoidable minimum. 



The following scheme represents the four main sub-classes and 

 their principal orders. By means of brackets placed on the right, 

 the (perhaps) more natural affinities of the sub-groups are indicated : — 



CLASS DEMOSPOXGIAE (Soll.) 



Grade I. Tetraxonida (Ldf.) 



Order 1. Camosa (Crtr.), Tops. 

 „ 2. Tetractinellida (Marshall). 



Grade II, Monaxonida (R. and D.) 



Order 3. Hadromerina (Tops.) 

 Sub-Order 1. Aciculina (Tops.) 

 Sub-Order 2. Clavulina (Vosm.) 



Order -4. Halichondrina (Vosm.) 



Grade III. Keratosa. 



Order 5. Dictyoceratina. 



,, 6. Dendroceratina. 



Grade IV. Myxospongida (Soll.) 



Family 1. Halisarcidae (O.S.) 

 „ 2. Oscarellidae (Ldf). 



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DETAILED CLASSIFICATION OF THE DEMOSPONGIAE. 



Grade I. Tetraxonida. 

 Demospongiae typically with tetraxon spicules. 



Order 1. Camosa (Crtr.), Tops, emend. 



Tetraxonida with tlie spicuKs greatly reduced in .size, and even want- 

 ing ; no diaetinal niega.scleres or triaenes M-ith long rlialxionies. 



Sub-Order 1. tMccROTRiAENOsA, Top.s. 



The eharacteristic spicules are triaene.s with sliort rlial»donie8, not 

 specially differentiated in tlie ectosonie or tlie elioano.sonie, and often 

 variously oinaniented or of aV)ei'rant types {(trnphitnaencs, mesotriaenes, 

 etc.) ; nlicroscIera'^ of various kind.s. A heterogeneous collection of 

 .sponges, of diverse attinities : "cliaiiions de cliaines l>risee.s, deriv(?8 san.s 

 iiilenuediaires connus " (Topsent). Not divided into families. Genera — 



+ Recent ami fossil. 



