THE PRIMORDIAL, OR CAMBRIAN AGE. 47 



have usually been described as sponges, but are more 

 probably partly of the nature of sponges and partly 

 " of that of Foraminifera. Of this kind are some of the 

 singular conical fossils described by Billings as Archceo- 

 cyathus, and found in the Primordial limestone of 

 Labrador. They are hollow within, with radiating 

 pores and plates, calcareous in some, and in others 

 with siliceous spicules like those of modern sponges. 

 Some of them are several inches in diameter, and they 

 must have grown rooted in muddy bottoms, in the 

 manner of some of the de«5p-sea sponges of modern 

 times. One species at least of these creatures was a 

 true Foraminifer, allied, though somewhat distantly, to 

 Eozoon. In some parts of the Primordial sandstones, 

 curious funnel-shaped casts in sand occur, sometimes 

 marked with spiral lines. The name Histioderma has 

 been given to some of these, and they have been 

 regarded as mouths of worm-burrows. Others of 

 larger size have been compared to inverted stumps 

 of trees. If they were produced by worms, some of 

 these must have been of gigantic size, but Billings 

 has recently suggested that they may be casts of 

 sponges that lived like some modern species imbedded 

 in the sand. In accordance with this view I have 

 represented these curious objects in the engraving. 

 On the whole, the life of these oldest Palaeozoic rocks 

 is not very abundant ; but there are probably represen- 

 tatives of three of the great subdivisions of animals — 

 or, as some would reckon them, of four — the Protozoa, 

 the Radiata (Coelenterata), the Mollusca, and the 



