GEOLOGICAL SURVEY OF THE TERRITORIES. 323 



up beneath a ledge of rock, with its skull lying undisturbed in the cen- 

 ter. A species distinguished for its small size and elegance is Clidastes 

 pttmiluSj Marsh. This little fellow was only 12 feet in length, and was 

 probably unable to avoid occasionally furnishing a meal for some of the 

 rapacious fishes which abounded in the same ocean. 



The flying saurians are pretty well known from the descriptions of 

 European authors. Our Mesozoic periods had been thought to have lacked 

 these singular forms until Professor Marsh and the writer discovered 

 remains of species in the Kansas chalk. Though these are not numer- 

 ous, their size was formidable. One of them, OrnWiocMrus harpyia, 

 Cope, spread eighteen feet between the tips of its wings, while the 0. 

 umbrosuSj Cope, covered nearly twenty- five feet with his expanse. These 

 strange creatures flapped their leathery wings over the waves, and often 

 plunging, s?ized many an unsuspecting fish ; or, soaring at a safe distance, 

 viewed the sports and combats of the more powerful saurians of the 

 sea. At night-fall, we may imagine them trooping to the shore, and 

 suspending themselves to the cliffs by the claw-bearing fingers of their 

 wing-limbs. 



Tortoises were the boatmen of the Cretaceous waters of the eastern 

 coast, but none had been known from the deposits of Kansas until very 

 recently. But two species are on record; one large and strange enough 

 to excite the attention of naturalists is the Frotostega gigas. Cope. 

 It is well known that the house or boat of the tortoise or turtle is formed 

 by the expansion of the usual bones of the skeleton till they meet and 

 unite, and thus become continuous. Thus the lower shell is formed of 

 united ribs of the breast and of the breast-bone, with bone deposited in the 

 skin. In the same way the roof is formed by the union of the ribs 

 with bone deposited in the skin. In the very young tortoise tJie ribs 

 are separate as in other animals ; as they grow older they begin to 

 expand at the upper side of the upper end, and with increased age the 

 expansion extends throughout the length. The ribs first come in con- 

 tact, where the process commences, and, in the land-tortoise, they are 

 united to the end. In the sea-turtle, the union ceases a little above the 

 ends. The fragments of the Frotostega were seen by one of my party 

 j)rojecting from a ledge of a low bluff. Their thinness and the distance 

 to which they were traced excited my curiosity, and I straightway 

 attacked the bank with the pick. After several square feet of rock had 

 been removed, we cleared up one floor, and found ourselves well repaid. 

 Many long slender pieces of two inches in width lay upon the ledge. 

 They were evidently ribs, with the usual heads, but behind each head 

 was a plate like the flattened bowl of a huge spoon, placed crosswise. 

 Beneath these stretched two broad plates, two feet in width, and no 

 thicker than binder's board. The edges were fingered, and the surface 

 hard and smooth. All this was quite new among full-grown animals, 

 and we at once determined that more ground must be explored lor 

 further light. After picking away the bank, and carving the soft rock, 

 new masses of strange bones were disclosed. Some bones of a large 

 paddle were recognized, and a leg-bone. The shoulder-blade of a huge 

 tortoise came next, and further examination showed that we had 

 stumbled on the burial-place of tlie largest species of sea-turtle yet 

 known. The single bones of the paddle were eight inches long, giving 

 the spread of the expanded flippers as considerably over fifteen feet. 

 But the ribs were tbose of an ordinary turtle just born, and the groat 

 plates represented the bony deposit in tbe skin, wliicli, commencing 

 independently in modern turtles, united with each other below at an 

 early day. liut it was incredibk^ that the largest ot known turtles 



