NORTH AMERICA AND THEIR VERTEBRATE FAUNA. I05 



which bones occur afford traces of very Httle that could have kept the animal 

 alive — tracks of worms, casts, borings, etc., a few crustaceans, like Estheria, 

 and cockroaches (Etoblattinna) — surely a very meager list. But, again, we 

 must recall that the animals are rarely embedded in their natural habitat. 

 This point is abundantly supported by the almost complete absence of any 

 tracks or foot -prints where the animals occur, and where abundant opportu- 

 nity was offered for the preservation of such impressions. The author has 

 searched diligently in the shales and mud stones of the Texas beds for many 

 days, and has found but a single foot-print of a vertebrate. Williston* 

 described some small foot-prints from a red shale near Abilene, in Taylor 

 County, Texas, which show 4 toes on the front foot and 5 behind. He 

 regards this as evidence that the animals were amphibians. The horizon is 

 regarded as probably Triassic by Dr. Williston, because it lies closely below 

 the Cretaceous. With this idea the author is not in accord. The beds from 

 which the tracks were found lie in the direct line of the southern extension 

 of the Clear Fork beds, and were so marked by Cummins. The Triassic does 

 not occur anywhere near so far east in this part of Texas. 



If, recognizing that the remains are not in their natural habitat, we turn 

 to more likely places of abode, probably at no great distance from the places 

 of interment of the bodies, the matter takes on a different aspect. In many 

 places in Texas the courses of old streams may be detected in the beds (plate 

 5, and plate 8, fig. i), and if we follow one of these in imagination a little 

 way back from the flat, swamp, playa, or lagoon into which it flowed, the 

 possibilities of invertebrate life are found to be much greater. From the Car- 

 boniferous rocks of Pennsylvania abundant remains of lowly insects, worms, 

 arachnids, crustaceans, decapods, and air-breathing gastropods have been 

 collected ; all exactly such forms of food as would be welcome to insectivorous 

 animals, or forms with the blunt crushing-teeth. Abundant occurrences of 

 cockroaches are reported by Sellards'-' from Pennsylvanian and Permian beds 

 in Kansas, and by Scudder," from West Virginia. 



The Clear Fork beds were never far from the ocean, nor free from the 

 danger of frequent and local incursions. Shells of Myalina occur in very thin 

 beds of limestone, 2 to 3 inches thick, in restricted areas, or even in beds of 

 clay, in close association with beds bearing vertebrates. 



In local areas in the more persistent beds of limestones occur some other 

 marine invertebrates which would have afforded abundant food for such 

 durophagous and conchifragous animals as may have frequented the shores 

 or even made excursions into the sea- waters, as do Coiiolophus and Sphenodon 

 to-day. It was in such conditions that the strong, chisel-like incisor-teeth 

 of Diadcctcs, or the strong, backwardly inclined incisors of Labidosaunis or 

 Captorhiiius, would be useful in tearing limpet-like forms from the rocks or 



» Williston, Biol. Bull., vol. XV, No. g, 1908, p. 238. 



'' SoUards, Kansas University Geological Survey, vol. ix, p. 501 



" Scudder, Bull. U. S. Geological Survey No. 124. 



