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XXIV.— PKELIMINAEY ACCOUNT OF THE TETKACTINELLID 

 SPONGES DBEDGED BY H.M.S. CHALLENGER, 

 1872-76. By PEOFESSOB W. J. SOLLAS, LL.D., 

 D. Sc. Part I. — The Choristida. 



[Presented, July 15, 1886.] 



The following short abstract of my forthcoming Report on the 

 Challenger Tetractinellid Sponges is published by kind permis- 

 sion of Dr. John Murray, Director of the Challenger Expedition 

 Reports : — 



Tkibe I.— TETRACTINELLIDA, Marshall. 



Skeleton characterized by quadri-radiate spicules, or "Lithistid" 

 sclerites. 



Order I. Choristida, Sollas. — Quadri-radiate spicules are 

 present, but not " Lithistid " sclerites. 



Order II. Lithistida, Zittel. — The chief skeleton consists of 

 "Lithistid" sclerites articulated to form a consistent network. 

 Quadri-radiate spicules may be present or not. 



Order 1. Choristida. 



Sub-order 1. Tetradina. — The chief spicules of the choano- 

 some are tetrads, amphitetrads, candelabra, or modified triana. 



Sub-order 2. Trianina. — The heads of the adult trianine 

 spicules are confined to the ectosome. 



Sub-order 1. Tetradina. 



Family 1. PLAKINID.ffi. — The canal system is eurypylous. 



Candelabra are present. 



Family 2. PACHASTRELLIM .— The canal system is either 

 eurypylous or aphodal. The tetrads are simple. 



Family 3. CORTICIDJE.— The canal system is aphodal ; the 

 characteristic tetrads are candelabra, or forks with trifurcate arms, 

 or forks with the surface ornamented by spines, or amphitetrads. 



SCIBN. PKOC. R.D.S. — VOL. V. PT. IV. 



