50 
THE SILURIAN BEACH. 
which were connected by a siphon. Some of the 
shells of this kind belonging to the Silurian de- 
posits are enormous : giants of the sea they must 
have been in those days. They have been found 
fifteen feet long, and as large round as a man’s 
body. One can imagine that the Cuttle-Fish in- 
habiting such a shell must have been a formi- 
dable animal. These straight chambered shells 
of the Silurian and Devonian seas are 
called Orthoceratites (see accompany- 
ing wood-cut). We shall meet them 
again hereafter, under another name 
and with a different form ; for, as they 
advance in the geological ages, they 
not only assume the curved outline with 
ever closer whorls till it culminates in 
the compact coil of the Ammonites of 
the middle periods, but the partitions, 
which are perfectly plain walls in these 
earlier forms, become scalloped and in- 
voluted along the edges in the later 
ones, making the most delicate and 
exquisite tracery on the surface of the 
shell. 
Of Articulates we find only two classes, Worms 
and Crustacea. Insects there were none, — for, 
as we have seen, this early world was wholly 
marine. There is little to be said of tho 
Worms, for their soft bodies, unprotected by 
