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XVI.— A CLASSIFICATION OF THE SPONGES. ByPBOFESSOE 

 SOLLAS, D.Sc, F.B.S.E., &c. 



[Read, June 15, 1885.] 



The Porifera are a phylum, divisible into the two classes — 



i. 1 Plethospongia3. n. Calcispongise. 



The Plethospongise may he subdivided into three sub-classes — 

 i. Hexactinellida. ii. 2 Demospongise. iii. Myxospongise. 



The Demospongise embrace the great majority of sponges, and 

 are divisible into the two tribes — the Monaxonida and Tetracti- 

 nellida. 



The Monaxonida include as orders — (1) the Monaxona (Monac- 

 tinellida, Auct.) and the Ceratosa, the latter clearly of polyphylitic 

 origin, and derived from several families of the former; (2) the 

 Tetractinellida include the orders Choristida (Sollas) and Lithis- 

 ida. 



The Myxospongise are not degenerate, but persistent askeletal 

 forms, and include two orders — Halisarcosa and Chondrosiosa 

 (excluding Corticium and its allies). 



The classification, as far as the orders, may stand thus : — 



POPJFERA (PHYLUM). 

 Class I. — Plethospongise. 



Sub- class i.-Hexactinellida. { ° EDEE 1--Lyssakma (Zittel) 



( ,, 2. — Dictyomna (Zittel). 



Tribe a. j ,, 1. — Monaxona. 



Monaxonida. ( ,, 2. — Ceratosa (Grant). 

 ,, ii. — Demospongise •' 



Tkibe b. i ,, 1.— Choristida (Sollas). 



Tetractinellida. ( ,, 2.— Lithistida (0. Scdt.). 



„ iii-Myxospongi,. { JcSSi ^^- 



Class II. — Calcispongiss. 



2 . — Chondrosiosa . 



1 ir\r]6os : a great numher or crowd. 2 Se/jLorypos : common. 



