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



By this demonstration Carter's classification of the Hexac- 

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

 endeavonrs to replace it Avith a new one. In this he lays 

 great stress on the growing together of the axial canals in 

 Sclerothammis. He conceives the Hexactinellida as having 

 originated from sponges like Oli/nthus, 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 [Sclerothamnus and fossil Hexactinel- 

 lida?), which subsequently broke up more or less completely. 

 into separate sexradiate spicules. 



In accordance with this conception, Marshall divides the 

 Hexactinellida into two groups : — 



1. Synauloid^. 



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. 



Sclerothamnus^ Marsh. 



II. ASYNAULOlD^. 



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 Asynauloidai are again divided into three families : — 



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

 radiate. Eurete^ Marsh. 



b. Pleionakidce^ 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^ 



Peripliragella^ Axdodictyon^ Fieldingia^ Aphrocal- 

 listes. 



c. Pollahidce. Hexactinellida with numerous forms of spi- 



* " Ideen liber die Verwandtschaftsverlialtnisse der Hexactinelliden," 

 /. c, Bd. sxTii. 



