REPORT ON THE DEEP-SEA KERATOSA. 



89 



of sponges. Certainly it is widely remote from being a true natural system, but the 

 same must be said of all other attempts at classification of sponges up to the most 

 recent times. All spongiologists who will judge critically, and compare the divisions 

 not dogmatically (like Polejaeff), will agree with this my view. 



Artificial Classification of Sponges founded on the Skeletal Structure. 



First Class. Malthospongi^e (or Malthosa). 



Porifera which possess no true mineral skeleton (composed of calcareous or siliceous 

 spicules), with or without spongin-skeleton, with or without pseudo-skeleton (composed 

 of xenophya). 



Order I. Myxospongi^e. — Without spongin-skeleton and without pseudo-skeleton 

 (Halisarcidse, Chondrosidse). 



Order II. Psammospongi^e. — Without spongin-skeleton, but with a pseudo-skeleton 



composed of xenophya (Ammoconidse, Psamminidse). 

 Order III. Ceraspongi^e. — With a true spongin-skeleton, with or without xenophya 



(Spongelidse, Stannomidse, Darwinellidas, Euspongidse, Aplysinidae). 



Second Class. Silicispongi^e (or Silicosa). 



Porifera which produce a true siliceous skeleton, composed of siliceous spicules 

 secreted by the sponge itself, with or without spongin-skeleton. 



Order IV. Demospongi^e (Monaxonidse and Tetractinellidae). — With simple (monaxial) 

 or four-rayed (tetraxial) siliceous spicules, with or without spongin-skeleton. 



Order V. Hyalospongi^e (Hexactinellidse). — With six-rayed and triaxial spicules, 

 without spongin-skeleton. 



Third Class. Calcispongi/E (or Calcarosa). 



Porifera which produce a true calcareous skeleton, composed of calcareous spicules 

 secreted by the sponge itself, with or without spongin-skeleton. 



Order VI. Ascospongi^ (Asconidse or Homoccelae). — Calcisponges without spongin- 

 skeleton, with tubular canal-system. 

 (zool. chall. EXP. — part lxxxii. — 1889.) Nnnn 12 



