ADAMS: SKULL OF THE WOLF-EEL. 339 



Opisthotic. (Plate XXVI, fig. 2; plate XXX, fig. 15.) 

 The opisthotics are small bones, rectangular in shape, very 

 thin and with two faces. They lie on the outer faces of the 

 exoccipitals, which have slight depressions to receive them. 

 The superior edges fit into grooves in the ventral part of the 

 pterotic. They extend posteriorly from the exoccipitals. 



Parietal. (Plate XXVI, fig. 2; plate XXVII, fig. 3; plate XXXIII, figs. 



49, 50, 51, 52.) 



The parietals and the pterotics are united in this skull, the 

 suture being entirely obliterated and showing only as a ridge 

 on the exterior face of the bone. The shape of the parietal, 

 considering it separately, is a little irregular. 



Outer Face. (Plate XXXIII, fig. 49.) 



The outer face is concave and smooth, with the exception of 

 the ridge marking the division line between pterotic and pa- 

 rietal. 



Articulations. 



The parietal has four articulations (considering it as a 

 separate bone). It articulates with the supraoccipital and 

 frontal on the inner face, its anterior edge being fitted in be- 

 tween the sphenotic and frontal; the ventral edge is joined to 

 the pterotic. 



Pterotic. (Plate XXVI, fig. 2; plate XXIX, fig. 11; plate XXXIII, figs. 



49, 50, 51, 52.) 



The pterotic is marked by a groove along the ventral part to 

 contain the articulating portion of the hyomandibular. Its 

 shape is triangular. 



hmer Face. (Plate XXXIII, fig. 50.) 



The inner face of the pterotic and parietal is divided, the 

 pterotic, or ventral half, forming a part of the brain-case, and 

 the dorsal half only an articulating surface. 



Outer Face. (Plate XXXIII, fig. 49.) 



The outer face is concave, smooth, and triangular in shape, 

 with the base ventral. The parietal is placed on the anterior 

 superior edge. 



Anterior Face. (Plate XXXIII, fig. 51.) 



The anterior face is at right angles to the outer face and has 

 a long ridge extending along its surface, forming a groove for 

 the hyomandibular. This face is roughly rectangular in shape. 



