270 M. K. A. Zittel on Fossil HexactinelUda. 



By this demonstration Carter's classification of tlie Hexac- 

 tinelUda is essentially shaken. Marshall, in a second memoir^'', 

 endeavours to replace it with a new one. In this he lay.s 

 great stress on the growing together of the axial canals in 

 Sclerothamnus. He conceives the Hexactineliida as having 

 originated from sponges like Olynthus^ in wliich parallel 

 lines of sarcode, crossing each other at right angles, were 

 formed in the syncytium, and thus produced a latticework 

 with cubical meshes. This sarcodic latticework was after- 

 Avards solidified by deposition of silica ; and, according to Mar- 

 shall, there were formed originally connected frameworks with 

 continuous axial canals [Sclerothammis and fossil Hexactinel- 

 iida ?) , which subsequently broke up more or less completely 

 into separate sexradiate s])icules. 



In accordance with this conception, Mar-shall divides the 

 Hexactineliida into two groups : — 



1. SYNAULOlDiE. 



The lumen of the tubes of the different spicules is continu- 

 ously connected like the latter themselves, so that the whole 

 latticed tissue of the sponge is permeated by a likewise con- 

 nected tubular system. 



Sclerothammis J Marsh. 



II. ASYNAULOiDiE. 



The lumen of the different spicules is never connected ; each 

 spicule, so far as the central fibre is concerned, is an indepen- 

 dently developed individual. 



The Asynauloidaj are again divided into three families : — 



a. Monakidce, with a single form of spicule, the pure sex- 

 radiate. Eurete, Marsh. 



b. Pleionahidce, with the principal mass of the skeleton 

 consisting of pure, fully developed sexradiates, but with these 

 brush-forked spicules, or rosettes, or both. The cubical form 

 predominates in the meshes of the skeleton. 



1. Spicules not soldered together: Lanuginella, Asho- 



nema. 



2. Spicules soldered together : Farrea, Dactylocalyx, 



Peri])lwageUa^ Auhdictyon, Fieldingia^ ApJirocal- 

 listes. 



c. PoUakidce. Hexactineliida with numerous forms of spi- 



* " Ideeu iiber die VerwandtschaftsYerluiltuisse der Hexactmelliden," 

 I. c. Bd. xxvii. 



