AND AVES OF NORTH AMERICA. 



122-e 



at first horizontally, then with a gradual approach to vertically. Like the other bones, 

 they are pneumatic and thin walled proximally ; at their medial portion they contain very 

 light spongy cancelli. 



As compared with Compsognathus the caudal vertebrae are very much shorter and 

 deeper : the extremities are stouter and more robust ; the metatarsi and phalanges with 

 ungues being shorter and thicker. 



That animals of this genus made some of the tracks similar to those of birds in the 

 red sandstones of the Valley of the Connecticut, there can be no doubt. It furthermore 

 explains some problematical impressions which are occasionally found with them. Tracks 

 of an animal resting in a plantigrade position, as indicated by the moulds of two long par- 

 allel metatarsi, each terminated by three toes, are accompanied by a peculiar bilobate, 

 transversely oval mark on the middle line, some distance behind the heels. 



Prof. Hitchcock states that it appears to be the impression of a short stiff tail. The 

 present specimen shows clearly that it was made by the obtuse extremities of the ischia. 

 The saurian squatted down, resting on its styloid iscbia as the third leg of a tripod of 

 which the anterior pair was represented by the hinder legs. Prof. 0. C. Marsh informs 

 me that in the museum of Yale College, a slab exhibiting impressions similar to the above, 

 shows the impressions of the anterior feet also, which were put to the ground in the act 

 of rising or sitting, or perhaps reached to it, while the animal was squatting, as do those 

 of carnivorous Mammalia. 



The tracks of many of the animals discovered by Hitchcock are plantigrade. That 

 they could not have walked like the plantigrade mammal, is sufficiently evident from the 

 length of the metatarsal elements, which would necessitate a constant contraction of the 

 tibialis anticus muscle, or peculiar arrangement of the tarsal bones, for its support. The 

 latter does not appear to have existed, and the former is so very improbable, that, in con- 

 nection with the pneumatic structure of the bones, there is abundant reason to suppose 

 that they progressed by leaps, and assumed the plantigrade position when at rest. 



No portion of the cranium or dentition of this genus lias been preserved. The large 

 stout hooked claws of the fore foot would indicate a more or less carnivorous diet. 



The Connecticut Sandstones have been regarded as Triassic, which the lower portions 

 of them undoubtedly are, and similar to the German Keuper in the presence of Labyrin- 

 thodonts, Thecodonts and Dinosauria in Massachusetts, Pennsylvania and North Carolina. 



MEGAD A CTYLTJS TOLYZELUS, Hitchcock. 



Loc. Cit. ]>. !!!), 1865. Ichnology of Massachusetts, p. 180, 1858. Tab. IX, fig. (i (Right fore foot). 

 This species was about the size of an ordinary hound. The surfaces of the vertebral arc smooth, and do not dis- 

 play any sculpture. Their dimensions arc as follows: 



Antcro-postenor length median caudal, 

 Depth articular face, 



Linen. 



10.1 



11.4 



