THE AGE OF INVERTEBRATES OF THE SEA. $i 



Mingan,^ and which probably belong to a large I.ithistid sponge 

 of that early time. The Lithistids have been recognised in the 



Fio. 31. — Astylospongia pyamorsa (Roemer). Niagara group. —After Hall. 



a. Spicules magnified. 



Upper Silurian and Carboniferous, and continuing upward to 

 the Cretaceous, these become vastly numerous, while their 



Fig. 32. — Spicules of Lithistid sponge {Trichospotigta of Billings). From the Cambrian 



of Labrador. 



modern representatives are by no means few. The silicious 

 sponges with simple spicules appear to have existed as far back 

 as the Carboniferous, and there is believed to be still earlier 



^ They probably belong to a large sponge named by Billings Tricho- 

 spongia sericea. 



E 2 



