lOO ROYAL SOCIETY OF CANADA 



all. or nearly all. these fossils belonc; — has been vastly increased by the 

 work of Prof. F. £. Sehulze. of Berlin, on the hexactinelled spono-es 

 di-etl^-ed \\\) by the Challen«>;er Expedition, and thus we are now better 

 enabled than hitherto to eoni])are the fossil and the recent tbrms." 



The conditions of accumulation of the Metis shales seem to have 

 been very favourable to the pyritization of organic remains. The shells 

 of Linnarssonia. small fragments of Trilobites and fronds of Alga\ seem, all 

 alike, to have been amenable to this change, and cylinders and sj^irals of 

 solid cr\-stallinc pyrite occupy the burrows of worms, while nodules of 

 the mineral destitute of any organic form also occur. On the other hand, 

 in some layers containing fossils, there is no trace of pyrite, but in these 

 it is very difficult to see the s])icules. owing to their similarity in colour 

 and lustre to the slate. 



Y. —Notices of the Several Species. 



The arrangement of Palaeozoic fossil sponges is still to some extent 

 provisional. That adopted below is the one most current at present, and 

 necessai'ily depends entirely on the material and structure of the skeleton. 



Viewed in this way, the whole of our Metis sponges, if we except a 

 few uncertain foi-ms to l)e mentioned in the sequel, belong to the order 

 Silicea, including those whi(di form their skeleton of siliceous needles or 

 spicules. Under this are sponges with sim])le spicules (Monactinellids), 

 and these seem to be the oldest of all, since the needles founil in the 

 Huronian cherts and those recognized by Mr. Matthew in the Laurentian 

 a])])ear to be mostly of this type. Others (Hexactinellids) present cruci- 

 loi'iu s])icules, or spicules with six rays, j)laced at right angles to each 

 other. These are arranged so that tlie rays are joined by their points, 

 forming very com])lex and beautiful frameworks, the variety of which 

 is increased by the fact that the diiïerent rays may be unequally de- 

 veloped, or some of them may be abortive, giving forms available for 

 a great many beautiful constructive uses. We shall find that the com- 

 plexil\' aiul diversity attainable by spicular forms, all based upon one 

 general law, but admitting of countless differences and modifications, had 

 already nearly reached ils maximum in a very early geological period. 



Tlie Hexactinellids may again be divided into two groups, according 

 to the united or loose condition of the sjiicides. When tliese are firmly 

 cemented together by silict-ous mailer, we have the group Dlctyonina, 

 and when they are united merely by animal mattei-, and consequently 

 fall asunder on decay, they l)elong to the gi-ou]> Lyssnkina. Under these 

 we have families, genera and species. 



The following list is a i-evision, with important additions, of that 

 jriven in 1889. 



