488 THE DEPTHS OF THE SEA. [cHaP. xX. 
oolite, where slabs are often found almost made up 
of them, with a characteristic deep-water association 
of Cidaris, Astrogonium, and Astropecten; and al- 
though not abundant in the English chalk, several 
species are found, and these show no tendency to 
degeneracy. As might be expected, such remains 
are rare in the shallow-water tertiaries. With regard 
to their distribution in modern seas, from the 
apparent abundance of P. asteria and P. miillert 
in deep water in the West Indies, and of P. wyville- 
thomsoni off the coast of Portugal, it is very pos- 
sible, as I have already said, that they may occupy 
a much more important place in the abyssal fauna 
than we at present imagine. 
Nearly all the additions from the deep water to 
the list of the Asteridea fall into the genera 
Archaster and Astropecten, or into the various sub- 
divisions of the old genus Goniaster. From their 
breaking up into a multitude of undistinguishable 
ossicles by the decomposition of their soft organic 
matter immediately after death, the fossil remains 
of star-fishes are comparatively rare, and are scarcely 
met with except in fine calcareous formations, such 
as the Wenlock limestone—and in later times in the 
fine yellow limestones of the oolites, and in the 
white chalk. In the latter formation, deposited ap- 
parently very much under the same circumstances 
as the Atlantic chalk-mud, the general character of 
the group of imbedded star-fishes is almost the same 
as in the modern fauna of the deep Atlantic. 
The Echinidea are a more typical order. From 
the compactness of their tests they are more readily 
preserved entire, and from the earliest periods their 
