100 



ROYAL siUCIETY OF CANADA 



all. or nearly all. tlu'so fossils l)eloni>; — ims i urn vastly increased bj- the 

 Avork of Prof. F. E. Seliul7,i'. of Berlin, on the hexaetinelled sponifes 

 (lre(l<i;e(l up hy tlie Challeni>er P^xpedltion, and thus we are now better 

 enabled than idfherto to compare the fossil and the i-ecent forms.' 



Tlie conditions (»f accumulation of the Metis shales seem to have 

 been very favourable to the ])vritization of orijanic remains. The sliells 

 of Linnarssonia. small frai;-ments of Trilobitesand frondsof Alga', seem, all 

 alike, to have been amenable to this change, and cylinders and spirals of 

 solid crvHtalline 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 ]ivrite. but in these 

 it is very ditticult to see the spicules, owing to their similarity in colour 

 and lustre to the sla*e. 



V. — NOTUKS OK THE SEVERAL SPECIES. 



The arrangement of Palaeozoic fossil s|)onges is still to some extent 

 provisional. That adojited below is the (me most current at present, and 

 necessarih' 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 forms to be mentioned in the secjuel, belong to the order 

 Silicca, including those which form their skeleton of siliceous needles or 

 spicules. Under this are sponges with simjilc spicules (Monactinellids), 

 and these seen', to be the oldest of all, since the needles found in the 

 Ilunmian cherts and those recognized by Mr. Matthew in the Laurcntian 

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

 form spicules, or spicules with six rays, ])laced at right angles to each 

 other. The.so are arranged so that tlie i-ays ar<' joined by their points, 

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

 is inci-eased by the fact that the ditterent i-ars may be unequally de- 

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

 a great nmny beautiful constructive uses. We shall tind that the com- 

 plexity and diversity attainable by spiculai- forms, all based upon one 

 general law, but admitting of countless ditferences and moditications, had 

 already nearly i-eadiecl its nuiximum in a very early geological period. 



The Hexactinellids may again bo divi<led into two groups, acioi'ding 

 to the united or loose condition of ihe spicules. When these are tirmly 

 cemented together by siliceous matter, we have the group Dicfyonma, 

 and when they are united merely by animal matter, and consequently 

 fall asunder on decay, they belong to the gi-oup /jjjssdkina. Under these 

 we have families, genera and species. 



The following list is u revision, with important additions, of that 

 given in 1889. 



