BY R. VON LENDENFELD, PH.D. 343 



4, FAMILY ECHISPID^E. 



Monactieerae, with an anastomosing network of horny fibi'es, 

 which contain biacerate or truncated spicules in their axis, and 

 are clad with truncate spicules, the points of which are free. 

 These spicules are always inserted at an angle of 45° and point 

 centrifusjallv. 



V. OPJ30 HYALOSPONGI^E. 



SPONGIiE, WITH A SKELETON COMPOSED OF SILICIOUS 

 SPICULES, WHICH HAVE ORIGINALLY BEEN FORMED AS 

 FLESH-SPICULES, AND AFTERWARDS MAY COALESCE TO FORM 

 HARD SKELETONS. 



1. FAMILY PLAKINIDyE. 



Hyalospongiae, with originally tetraradiate spicules, which do 

 not coalesce but tend to become biacerate. 



2. FAMILY HEXACTTNELLID^. 



Hyalospongiae, with hexar-adiate spicules, which partly coalesce. 

 Without a drainage canal system the large sack-shaped ciliated 

 chambers open direct into a large oscular tube, which is closed at 

 the osculum by a silicious net work. 



3. FAMILY TETRACTINELLID^E. 



Hyalospongiae, with loose tetraradiate spicules, which are of 

 variable shape, and partly tend to coalesce, with an outer hard 

 layer containing dense masses of Flesh-spicules and often with 

 subdermal crypts. 



4. FAMILY LITHISTID^E. 



Hyalospongiae, with a skeleton, consisting of dense hard silica, 

 which is developed by the coalescing of tetraradiate spicules. 

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