NATURAL SCIENCES OP PHILADELPHIA. 241 



the jaw with teeth, in the Academy's Museum, the Bathygnathus borealis 

 of Leidy, has left its remains in the red sandstone of Prince Edward's Island, of 

 the same age, and we safely conclude that some of the large-clawed biped 

 tracks of Hitchcock are those of that animal. Dr. Leidy has suspected that 

 this would jirove to be the case, as he asks* "was this animal probably not one 

 of the bipeds which made the so-called bird tracks in the sandstone of the 

 Connecticut vallej^?" This enquiry was, after an examination of the form of 

 Laelaps, answered in the affirmative. f I have ascribed these tracks to reptiles 

 allied to Lielaps, and Huxley believes also that they were made by Dino- 

 sauria.J 



The creatures which strode along the flats of the Triassic estuary have been 

 various in species and genera, as pointed out by Hitchcock. Some were pure- 

 ly biped ; some occasionally supported themselves on a pair of reduced fore- 

 limbs. There are impressions where these creatures have squatted on their 

 haunches. One can well imagine the singular effect which these huge grega- 

 rious reptiles would produce, standing motionless, goblin-like, on a horizon 

 lit by a full moon ; or lying with outstretched neck and ponderous haunches 

 basking in the noonday sun ; or marching or wading slowlj^ along the water's 

 edge, ready for a plunge at passing fishes or swimming reptiles. But in the 

 active pursuit of terrestrial prey did such an animal as the Lalaps run like the 

 Ostrich, or leap like the Kangaroo ? So far as the Triassic tracks go, there is 

 no evidence of leapers, only runners, fell upon an exhausted quarry. Or were 

 they only carrion eaters, tearing and devouring the dead of age and disease ? 

 Probably some were such, but the prehensile claws of La?laps are like instru- 

 ments for holding living prey. 



Leelaps has a long femur ; those great leapers the Kangaroos have a short 

 one ; the cursorial birds, however, have a similar form of femur, but they do 

 not leap. So this form is not conclusive. The modern Iguanas have long 

 femora, and they all progress by their simultaneous motion ; they only leap ; 

 but man with his long femur runs only. The question then does not depend 

 on the form of the femur. 



I have suggested on a former occasion that La^laps took enormous leaps and 

 struck its prey with its hind limits. I say, in describing it, " The small size of 

 the fore limbs must have rendered them far less efficient as weapons than the 

 hind feet, in an attack on such a creature as Hadrosanrus ; hence perhaps the 

 latter were preferred in inflicting fatal wounds. The ornithic type of sacrum 

 elucidated by Prof. Owen suggests a resemblance in the use of the limb." 



The lightness and hollowness of the bones of the Lfelaps iirrest the attention. 

 This is especially true of the long bones of the hind limbs; those of the fore 

 limbs have a less considerable medullar}' cavity. In this respect they are 

 quite similar to those of Crelosaurus Leidy, of which its describer remarks, 

 "that the medullary cavitj' of the tibia is large, and the walls thin and 

 dense," " being intermediate in this respect between the characters of the 

 mammals and birds." 



The mutual flexute, as well as the lightness and strength of the great femur 

 and tibia, are altogether appropriate to great powers of leaping. The feet 

 must have been elongate, whatever the form of the tarsi; the phalanges, or 

 finger bones, were slender, nearly as much so relatively as those of an eagle, 

 while the great claws in which they terminated were relatively larger and more 

 compressed than in the birds of prey. There was no provision for the retrac- 

 tibility observed in the great carnivorous mammalia, but the size of the infe- 

 rior basal tuberosity indicates the insertion of a great tendon of a powerful 

 flexor muscle. The slight grooves at the base, and deeper one on each side 

 of the phalange, suggest the usual horny sheath, which, prolonging the point 

 of the claw, would give it a total length of eleven inches. 



* Journal Acad. Nat. Sciences, 1854, 329. 



t American Natufalist, 1807, ^^7. Hay's Medical News and Reporter, 1868. 



JProceedings Royal Society, London, 1808, p. Natural Science Review, 1868. 



1868.] 



