﻿EOCENE PERIOD 137 



Owing to defects in the geological record fish-life seems 

 to have suddenly attained a decidedly modern aspect. 

 " Writ in water " largely applies to fish genealogies. And 

 indeed practically all life is met with in the Eocene after a 

 break in its history. 



Among the invertebrate marine masses, crabs exhibited crabs 

 considerable development. Swimming crabs (Portunites), 

 long-beaked spider-crabs (Oxyrhyncha), sharp-nosed crabs 

 (Matuta), and crabs in carapaces shaped like that of the 

 modern land-crab (Catometopa) were all in evidence. Hermit- 

 crabs — classed, on account of their long tails, with lobsters — 

 had also made their appearance (Paguridce). 



A remnant of Ammonites lived on, but their annals soon cephalopods 

 ■closed. Belemnites were represented only by a few forms 

 with the internal shell much reduced in size. Some of them 

 seem to have been becoming very much like the ordinary 

 sepia or cuttle-fish of our own times (Belosepia). Others 

 resembled those modern cuttle-fishes in which the shell has 

 almost disappeared (Spirula). Nautili continued prosperous, 

 and were thus restored, after a long eclipse, to a position of 

 importance among cephalopods. 



Gastropods were assuming a modern aspect. Siphoned univalved 

 forms, which had been improving their position ever since molluscs 

 the Trias, were now the prevailing type — whelks (Buccinuni), 

 cowries (Cyprcza), mitre-shells (Mitra), and olive-shells 

 (Oliva) being in great force. Some forms were living in 

 turreted shells half a yard in length (Ceritheum). Old- 

 fashioned siphonless sea-snails, although relatively quite 

 unimportant, were well represented by some old genera that 

 had held on from the Trias {Natica, etc.). 



Chitons were now of modern type, with the shell plates 

 well attached to the margin of the mantle (Ischnochitonidce). 



Many genera of bivalved molluscs had now been super- bivalved 

 seded by modified forms. Existing genera of mussels (Ano- molluscs 

 donta), sponge-borers (Vulsella), and various burrowing bivalves 

 had become distinct (Cytherea, etc.) : and clams approximated 

 much more to living forms (Byssocardium, Lithocardium). 



Lampshells, so far at least as regards reduction of families, lampshells 

 .now rested on the bed-rock of their depression. 



