LIFE 



421 



-tern and southern interior throughout the whole Devonian period. 

 On the other hand, a notable number of species were common to it 



Id to the northwestern province. 

 Life of Land Waters 

 Certain Devonian formations, such as the "Old Red Sandstone" 

 and the C'atskill formation, appear to be composed of deposits laid 

 down in more or less local lodgment basins that were progressively 

 tilled by land-wash and fresh-water sediments. These basins appear 

 to have been the home of a fresh- or brackish-water fauna, among 

 which fishes, crustaceans, and ostracoderms were conspicuous. 

 Perhaps the geological record presents no more suggestive combina- 

 tion of ancient life. The type of the fauna was foreshadowed by the 

 eurypterids and fishes, or fish-like forms of the late Silurian; but 

 record of that time is less perfect than that of the late Devonian. 

 The center of interest in this fauna is found in the ostracoderms 

 gs. 368 and 369), a class of animals between arthropods and 



? ig. 368. Restoration of Cephclaspis, seen from the side. (After Patten.) 



vertebrates. Their chief interest lies in their suggestion that 

 vertebrates sprang from arthropods. The ostracoderms bear ex- 

 ternal resemblances, in the head and trunk, to trilobites and king- 

 crabs, while some of them have caudal fins and fish-like bodies. 

 They were formerly classed as fishes, but no vertebrae have been 

 found, or appendages or jaws of the vertebrate type. Ostracoderms 

 probably formed the climax and almost the end of their own strange 

 race, for they practically disappeared with this period. This is not 

 surprising in view of the development of powerful fishes, for the 

 ostracoderms were obviously not a masterful race. Besides being 

 small, they were clumsy, and their mouth-parts were weak. They 

 probably plowed the soft bottoms of the sluggish waters, half buried 

 in the mud, above which little beside their peculiarly placed eyes 

 and the backs of the plated bucklers were habitually exposed. 



Another class of strange organisms related to the fishes, but not 



I 



