124 Notice of Dr. MantelVs Medals of Creation. 



England ; and it is inferred that a very equal warm temperature 

 must at an early epoch have pervaded the globe, whereas " the 

 reef-forming genera of corals are now confined to waters where 

 the temperature is not below 70° ; their most prolific develop- 

 ment being 76°."* 



The fossil Echinodermata {spiny-skin animals) are found 

 among the earliest traces of animal existence ; the Crinoidea 

 abound in the Silurian system, and one species of Stelleridse has 

 been there found. 



These animals have a radiated structure around a common 

 centre, of which the sea-urchin or hedgehog, and the star-fishes 

 of our sea-coasts are familiar examples. In most cases the skin 

 is protected by spines — whence their name ; and there are mi- 

 nute foraminss for the admission of sea-water or the protrusion 

 and retraction of minute tubes or hollow tentacula, which con- 

 stitute their common organs of adhesion and locomotion. 



In England, in North America, and many other parts of the 

 world, entire mountain chains are composed chiefly of the bones of 

 Crinoidea. " The Crinoidea may be regarded as star-fishes, fixed, 

 to one spot by a jointed stem ; the star-fishes are free Crinoidea." 



The British species of Crinoidea exceed 130 ; the skeleton of 

 an individual lily encrinite is composed of more than 26,000 

 pieces or little bones, and a single pentacrinite of upwards of 

 150,000, so that the number and variety, and we may add, beau- 

 ty of these fossils will no longer appear marvellous. 



Fossil Echini have not been observed in the Silurian system; 

 but the Cidaris appear in the carboniferous. In the lias. Echini 

 begin to prevail with Stelleridas and become abundant in the 

 oolite and chalk. In the marine tertiary they are as numerous 

 as in the modern deposits. In the British strata nearly 100 Echini 

 have been obtained, almost all of extinct species, while hardly 20 

 species of star-fishes have been observed. 



The Fossil Mollusca are (except the animalcules) by far the 

 most numerous and various family of organic remains. To the 

 mere amateur conchologist, shells are objects of great interest on 

 account of their beautiful forms and colors, but few collectors 

 are conversant with the nature of the animals that secreted and 



* Or between 72° and 80°; different corals probably are favored by different 

 temperatures. — Eds. 



