OLD-WORLD FORMS 41 



link would be brought to light. This has hardly 

 proved to be the case. In certain groups animals 

 hitherto known only as extinct, such as the stalked 

 crinoids and certain Crustacea e.g., the Eryonidae 

 have been shown to be still extant. The remarkable 

 Cephalodiscus and Rhabdopleura, with their remote ver- 

 tebrate affinities, have been dragged from their dark 

 retreats. Haeckel regards certain of the deep-sea 

 medusae as archaic, and perhaps the same is true of 

 the ascidians and holothurians ; but, on the whole, the 

 deep-sea fauna cannot be regarded as older than 

 the other faunas of the seas. The hopes that were 

 cherished of finding living ichthyosauri or plesiosauri, 

 or the Devonian ganoid fishes, or at least a trilobite, 

 or some of those curious fossil echinoderms, the 

 cystoids and blastoids, must be given up. Certain 

 of the larger groups peculiar to the deep sea have 

 probably been there since remote times ; but many of 

 the inhabitants of the deep belong to the same families, 

 and even to the same genera, as their shallow-water 

 allies, and have probably descended in more recent 

 times. There, in the deep dark stillness of the ocean 

 bed, unruffled by secular change, they have developed 

 and are developing new modifications and new forms, 

 which are as characteristic of the deep sea as an Alpine 

 fauna is of the mountain heights. 



