THE OLDEST AIR-BREATHERS 2/3 



in each case, it is often impossible in breaking up the hard 

 matrix to recover more than a portion of them. The original 

 description by Owen was therefore based on somewhat imperfect 

 material, but additional specimens subsequently found have 

 supplemented it in such a manner as to enable us somewhat 

 completely to restore in imagination the form of the animal, 

 which, though much smaller than Baphetes^ agrees with it in its 

 sculptured bones, in its bony armature, especially beneath, and 

 in its plicated teeth. 



In form, Dendrerpeton Acadianum was probably lizard-like ; 

 with a broad flat head, short stout limbs and an elongated tail ; 

 and having its skin, and more particularly that of the belly, 

 protected by small bony plates closely overlapping each other, 

 and arranged en chevron^ in oblique rows meeting on the 

 mesial line, where in front was a thoracic plate. It may have 

 attained the length of two feet. The form of the head is not 

 unlike that of Baphetes^ but longer in proportion ; and much 

 resembles that of the labyrinthodont reptiles of the Trias. 

 The bones of the skull are sculptured as in Baphetes^ but in a 

 smaller pattern. 



The fore hmb of the adult animal, including the toes, 

 must have been four or five inches in length, and is of 

 massive proportions. The bones were hollow, and in the case 

 of the phalanges the bony walls were thin, so that they are 

 often crushed flat. The humerus, or arm bone, however, was 

 a strong bone, with thick walls and a cancellated structure 

 toward its extremities ; still even these have sometimes yielded 

 to, the great pressure to which they have been subjected. The 

 cavity of the interior of the limb bones is usually filled with 

 calcspar stained with organic matter, but showing no struc- 

 ture ; and the inner side of the bony wall is smooth without 

 any indication of cartilaginous matter lining it. 



The vertebrae, in the external aspect of their bodies, remind 

 one of those of fishes, expanding toward the extremities, and 



