CARBONIFEROUS PERIOD 57 



crabs were still to come ; but their advent was foreshadowed 

 by various forms more or less resembling opossum-shrimps 

 (Anthrapal&mon, etc.)- Other animals, slightly carapaced, 

 bore a close resemblance to mantis-shrimps (Necroscylla) ; 

 some (Praanaspides, Woodward), wholly without carapace, 

 resembled the mountain-shrimps now dwelling in rock-pools 

 of Tasmania (Anaspides). 



Time had brought many changes among creatures above 

 the rank of invertebrates. The flat-headed, prickly 

 skinned little fishes, and several other Devonian types, 

 allied probably to sharks, had now died out. All the quaintly 

 armoured semi-fishes had also become extinct ; and a like 

 fate had overtaken the armoured fishes with jointed necks 

 (Arthrodira). There seems, indeed, to have been a process of 

 disarmament in operation ; and fishes, instead of being 

 provided with heavy protection for the skin, were to have 

 their gristly internal framework strengthened, and their 

 swimming powers improved. 



Shark-like fishes were very numerous and widespread. SHARKS 

 Some of these (Acanthodes) were small creatures, less than a 

 foot in length, and belonged to a family first in view in 

 Devonian seas. These newer forms were probably quicker 

 in guiding movements, owing to the enlargement of the 

 breast-fins. Numerous blunt crushing teeth have also been 

 found, which belonged probably to sharks more or less 

 resembling the mollusc-eating Port Jackson sharks of our 

 own day (Cochliodus'). There were also fishes that appear 

 to have been diverging from sharks in the direction of rays 

 or skates (Tamiobatis) : and a species of the family (Raiido) SKATES 

 seems already to have been in existence (Petalodus). In 

 addition to these there were some strange-looking forms 

 that appear to have been intermediate in development 

 between sharks and dipnoans or lung-fishes (Pleuracanthus). 



Lung-fishes were more fully represented : but the new DIPNOANS 

 forms, except in being as a rule of larger size, differed but 

 little from their Devonian ancestors (Ctenodus). 



Numerous modifications were going on in the ranks of CROSSOPT- 

 the ganoids. Among the fringe-finned forms characterised, ERYGIAN 

 among other things, by paddle-like fins, none of the known GANOIDS 



