STONE-LILIES. 157 



which range from the lower Silurian or Ordovician epoch 

 to the present day. The parallelism in this respect is not, 

 however, so close as it might at first sight appear, since the 

 lower Palaeozoic representatives of both the latter genera 

 are subgenerically distinct from their living analogues. 

 While the first of these two genera has some ten living 

 species, the latter possesses but five, and both had a large 

 number of Palaeozoic representatives. 



It is, perhaps, almost superfluous to add that the whole 

 of the brachiopods are a waning group, although the types 

 known as rhynchonellas and terebratulas have been ascer- 

 tained, of recent years, to be more numerously represented, 

 both as regards species and individuals, than was formerly 

 considered to be the case. 



The so-called stone-lilies, or crinoids near relatives of 

 the familiar star-fish, but attached, in the young condition 

 at least, to the sea -bottom by a jointed stem likewise 

 constitute a group in which by far the greater number of 

 types are totally extinct, although a few survive to merit 

 the title heading the present chapter. The stone-lilies are 

 divided into two primary groups, one of which is totally 

 extinct, while the other, which does not extend backwards 

 beyond the Secondary period, comprises the few existing 

 representatives of the class. The genus which may be 

 selected as especially worthy of the designation " living 

 fossil " is Fentacrinus, so named from the pentagonal form 

 of the discs of the stalk so familiar to all who have 

 studied the fossils of the British Secondary rocks. The 

 pentacrinids were originally named on the evidence of 

 certain species from the British lias, which attained a 

 height of several feet, and flourished in extraordinary 

 profusion on the old sea-bottom, as the reader who cares 

 to pay a visit to the fossil galleries of the Natural History 

 Museum may see for himself. For some time the group 

 was only known from the Secondary rocks, but eventually 

 a minute species (P. europaus), supposed to belong to it, 

 was found living in deep water off the Irish coast ; while 

 in 1755 a much larger form (P. caput-medusce] was dis- 

 covered in the We-t Indian seas. The former turned out, 

 however, to be merely the larva of the familiar feather-star 



