Stromatoporoids and Eozoon. 343 



framework to that of a Dlctyonine sponge. Beatricea was 

 compared to an rthocerasAWs.^ mollusc. 



I myself at first mistook altered cliitinous rings and coils 

 for siliceous spicules, the astrorliizse for oscnles, and the 

 tabular for dia|)hragms and dissepiments like those of CUona, 

 and regarded the general skeletal framework as an originally 

 spicular structure altered by mineralization, for I could often 

 see rings and apparent sigmas imbedded in it. I found 

 later, however, that the supposed "spicules^' were altered 

 chitinous hoops and spirals. Tiie astrorliizte appear to be due to 

 the fusion of several outer openings of tubuli, thereby leading 

 to the converging of finer pseudopods into main trunks. 

 J^l. IX. figs. 13, 14, representing a longitudinal vertical 

 section of Polytrema ci/h'ndncum, shows, for instance, tubuli 

 with a relatively large single external opening and one, two, 

 or tliree smaller inner openings, a compound system being 

 funnel-shaped with a cribriform mouth directed inwards. A 

 growth and extension of this simple system would result in 

 the formation of an astrorhiza. Further, a more careful 

 examination revealed the typical Foraminiferal structure of 

 the skeleton itself. 



What chiefly led me to regard the Stromatoporoids as 

 siliceous sponges was the discovery, in the sections of those 

 fossils, of little " pockets " of coiled sigma-like bodies and also 

 tubular canals lined with these bodies in scalariform fashion. 

 I had seen a somewhat similar arrangement of ring-like real 

 siliceous spicules in the sponge part of " Merlia normani,^^ 

 which at one stage of my devious gropings after the clue 

 to this mystery I had named NoronJia scalariformis. But 

 presently I found similarly shaped rings in the soft tissues 

 of decalcified recent Foraminifera *. Here the chitin has 

 resisted the acid used for decalcifying, and the rings seemed 

 to be chitinous, but in the fossils they looked like siliceous 

 spicules. I now examined the skeletal framework, and saw 

 that it was penetrated by tubuli and channels of communi- 

 cation between chambers. 



The so-called tabulse, which were supposed by Nicholson 

 to be similar to those of Millepoi'a, are diaphragms formed in 

 the chambers and in tlie course of the canals. 



Tuese " tabulae" are present in the spaces filled by the soft 

 tissues, both in the Stromatopora type and in i\\e. Actinostroma 



* Evidently the function of tlie chitinous hoops and coils is to give 

 support to the soft raonilated branching sarcode. The swellings on many 

 of them are due apparently to lateral compression arising from the pull 

 of the extensile sarcode along nn axis at right angles to the plane of the 

 hoops. 



