i2 4 SCIENCE PROGRESS 



Amphibians, which in the late-Palaeozoic era were dominantly 

 represented by the armoured Labyrinthodonts or Stegocephalia. 

 Yet at the present day armour is conspicuously absent from the 

 naked skin of frogs, toads, newts and salamanders, occurring 

 only in the form of small, flexible scales embedded in the 

 integument of the worm-like Cascilians ; the horns of the horned 

 toad (Ceratophrys) are almost the only instance of superficial, 

 bony plates occurring in modern Amphibians. In the Palaeozoic 

 era, however, we find that side by side with armoured forms 

 such as Cricotus, Anthracosaurus and Secleya there existed 

 naked forms, from which the modern Amphibians are doubt- 

 less descended. Thus in a single family — the Dolichosomatidce — 

 we find a naked form like Dolichosoma (from which the modern 

 Apoda are supposed by Fritsch 1 to be derived), as well as an 

 armoured form — Ophidcrpcton — with both dorsal and ventral 

 scutes. 



Chelonians are perhaps the most typically armoured class of 

 Vertebrates at the present time ; yet some of the largest and 

 most active forms, such as the leathery turtles {Dcrmochclys or 

 Sphargis)? have largely discarded armour, for they possess no 

 tessellated plastron and their carapace is thin and devoid of 

 epidermal shields. But an earlier form of this group, viz. the 

 Eocene Psephophoms (nearly 10 ft. in length), not only has also 

 a completely tessellated carapace and plastron but exhibits 

 marginal ossifications which are absent in the existing leathery 

 turtle. In the highly specialised, carnivorous and therefore 

 particularly active group of mud turtles (Trionyx, Emyda, etc.), 

 the integument likewise develops no epidermal shields and 

 is quite soft, whilst the plastron is always separate from the 

 carapace. 



Chelonians also furnish a striking instance of the inevitable 

 dying-out of forms which have developed extensive, massive 

 or complicated armour, as in the case of the great bizarre 

 horned tortoises (Miolania), found in the Pleistocene of 

 Australia, Lord Howe's Island and Patagonia, in which even 

 the tail was enclosed in a thick, knobbed, bony sheath. The 

 same tendency is exemplified, in a less degree, by the gigantic 



1 Fauna der Gaskohle und der Kalksteinc der Pcrmformation Bohmcns, 1 883-6. 



2 A recent specimen measured by Mr. Lucas {Nature, February 11, 1909) 

 reached 6 ft. 10 in. from nose to tail along the curve, and 8 ft. 9 in. from tip to tip 

 of the flippers across the shoulders. 



