FISHES. 159 



dredging it was, however, found that pentacrinids were 

 really abundant in certain localities, and several new 

 species (one of which is represented in the accompanying 

 figure) have been named of late years. Thus in the 

 summer of 1870, Gwyn Jeffreys dredged up quantities in 

 the Atlantic; while in the neighbourhood of the Aru Islands 

 Moseley tells us that during the voyage of the Challenger 

 more than thirty specimens of Pentacrinus were taken 

 at a single haul of the dredge in 500 fathoms of water. 

 Although their pyritized remains, which are so common on 

 the slabs of lias, would have indicated that these crinoids 

 must have been creatures of extreme beauty, no adequate 

 idea of their gracefulness would ever have been obtained 

 had the group not been represented in the living state. 



Pentacrinids are, however, by no means the only " living 

 fossils " belonging to this class of animals. For instance, 

 the smaller and simpler Rhizocrinus of the Atlantic is a 

 survivor from the Eocene ; while both this genus and the 

 allied Bathycrinus, from depths reaching to 2400 fathoms 

 in the Atlantic, are near relatives of the extinct Bourgueti- 

 crinus of the chalk. Moreover, all these forms are related 

 to the so-called pear-encrinites (Apiocrinus), so common 

 in the middle Jurassic rocks of Europe ; while these, 

 again, lead on to the still earlier lily-encrinites (Encrinus) 

 of the trias. 



If space permitted, there are several other groups of 

 invertebrates which might claim our attention, but we must 

 pass on to the vertebrates. Among the fishes the one 

 which has the greatest claim to the title of a " living 

 fossil" is the aforesaid Australian lung-fish of the rivers 

 of Queensland. As mentioned in the last chapter, teeth 

 of fishes allied to the Australian lung-fish have been long 

 known from the Secondary rocks, ranging downwards to 

 the trias, and occurring in Europe, India, Africa, and 

 North America. These teeth were, indeed, first described 

 by Agassiz as far back as the year 1838 ; and the group 

 was believed to be extinct till 1870, when one of the two 

 living forms was discovered. At first, as stated in the 

 same chapter, it was believed that the latter were 

 generically identical with the fossil, Geratodus, but it has 



