216 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



the sketch (Plate 12, Fig. 2), whicli is copied from the only slab 

 yet found with the tracks of this animal. The number of toes 

 directed forward, and especially the number of phalangeal impres- 

 sions, forbid us to class it among birds. There is, however, some 

 resemblance between its foot and that of a frog in an embryotic 

 state ; and such analogies are important, because the adult devel- 

 opments of the early geological periods correspond best to the 

 embryo structure of living animals. Hence there is at least a 

 probability, that this animal was a biped batrachian ; and what 

 a monster, with feet 20 inches long and 12 wide ! No such biped 

 batrachians, indeed, now live ; but some exist with only two feet. 

 For an animal so large, its tracks are more nearly in a right line 

 than we should expect, and its steps shorter ; an indication of short 

 legs. 



In the American Journal of Science, Vol. IV. of the New Se- 

 ries, I have given full details respecting this track and its affin- 

 ities. But I do not judge it expedient to repeat them all here. 

 And yet so remarkable an animal — the most extraordinary of all 

 those discovered by their tracks — could not properly be passed in 

 silence in an attempt to give a monograph of this subject. Al- 

 though a sketch of the slab containing the tracks of this species 

 is given in that work, yet I have thought its exhibition here would 

 be appropriate ; and it is accordingly given on Plate 12, fig. 2, re- 

 duced eighteen diameters. It contains four tracks of the Otozoum, 

 of which A is the most perfect. The two rows of tracks, a, a, Sec, 

 b, b, &;c., belong to the Brontozoum ■parallelum ; besides which a 

 large part of the surface is covered with rain-drops in relief, as are 

 all the tracks. 



