488 THE DEPTHS OF THE SEA. [chap. x. 



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 exj^ected, 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. mulleri 

 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 Goni aster. Prom their 

 breaking up into a multitude of un distinguishable 

 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 vellow 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. Prom 

 the compactness of their tests they are more readily 

 preserved entire, and from the earliest periods their 



