THE DEEP-SEA FAU^TA. 169 



corals, solitary forms usually, are often dredged in great num- 

 bers, and are in striking contrast to the extensive coral reefs of 

 former geological periods, which resemble those of recent times, 

 and must have flourished in shallow water under conditions of 

 temperature analogous to those of the districts in which coral 

 reefs are found to-day. 



The Echini characteristic of the shallower littoral districts 

 were formerly, as now, mainly Clypeastridse, while the Echinidae, 

 Cidaridse, Diadematida?, and Coelopleuridae characterized the con- 

 tinental areas, and the Ananchytidse, Pourtalesise, Phormosomse, 

 and Galeritidse probably flourished best in deep water. 



Lingula may have been from the earliest times a littoral 

 species, wdiile Terebratula and other brachiopods belonged to 

 the continental and abyssal regions. Gasteropods are found in 

 deep water, but are usually of small size. The larger species 

 seem to have lived, as to-day, in comparatively shaUow areas, 

 though a few, such as Voluta, Dentalium, and Pleurotomaria, 

 lived in deep water. Of the cephalopods many are pelagic, 

 others littoral, while Nautilus and Sf)ii'ula are deep-sea types, 

 though Verrill has dredged sheUs of the pelagic argonaut in 

 deep water. In the older formations the huge cephaloj)ods of 

 these times were abundant in the littoral regions. 



Among the Crustacea Eryon-like forms predominate in deep 

 waters, and gigantic isopods and Pygnogonidse are also found at 

 great depths. Accumulations of terrestrial animals and plants 

 driven out to sea by the winds and currents may likewise find 

 their way to deep-sea deposits. 



The remains of pelagic animals, often occurring in great 

 numbers, do not always indicate an oceanic deposit, as they may 

 after their death be taken by the winds and currents far from 

 their habitat, and be carried considerable distances by fishes. 

 The shell of Spirula is found on all tropical beaches. We find 

 immense accumulations of pelagic animals, as well as of the 

 dead carcasses of squids, driven ashore in quantities by storms 

 or caught by the tides. The mortality among fishes is often 

 very great ; large shoals are hunted to the shore by predatory 

 species and sharks, and our beaches are not unfrequently lined 

 for long distances with fishes which have perished from sudden 

 unknown causes. 



