4o8 Bulletin American Museum of Natural History. [Vol. XIX, 



The length of the head, from the apex of the snout to a line 

 joining the hinder borders of the lateral spines, is 35 mm. 

 The apex of the snout is rounded and only 3.5 mm. wide. 

 The skull lies with the upper surface toward the viewer. The 

 bones are so closely united that their limits cannot be dis- 

 tinguished. The surface is almost everywhere covered with 

 tubercles, sometimes scattered, but usually arranged in rows 

 more or less regular. A few of those on the upper surface of 

 the snout form short spines. 



Along the borders of the snout, for about 20 mm., there are 

 seen, at intervals of two or three millimeters, what appear to 

 be teeth, but which are possibly only enlarged marginal 

 tubercles. Between the larger ones are others of smaller size. 

 Some medium-sized ones are found at the apex of the snout. 

 At a considerable distance behind the head is seen a stout 

 bone bearing four or five teeth larger than those of the ros- 

 trum, the largest about 1.5 mm. in length. This bone seems 

 to the writer to be a portion of the lower jaw, which has 

 been displaced. 



As may be seen from PI. xxvi, Fig. 2, orh., there are, 

 between the bases of the spines, two rings of bone. These 

 appear to be the sclerotic rings and to indicate the position 

 of the eyes; but, incomprehensibly enough, these have been 

 overlain by some bones of the upper surface of the skull. 

 The appearances of the fossil are not consistent with the sup- 

 position that the lower surface of the head is presented. There 

 is probably some distortion here. 



Behind the bases of the spines the fossil contracts for about 

 10 mm. Whether this region belongs to the skull or not is 

 not easily decided. There appear to be five bones here, an 

 elongated median one, extending the full length of the area, 

 and two others on each side. Of the latter, the hindermost 

 sends an arm forward along the outside of the more anterior 

 one. These bones can be distinguished on the specimens only 

 by close inspection. 



Behind the area mentioned, at a, PI. xxvii, Fig. 2, there 

 is a bony mass whose surface is covered with ridges which 

 converge to a point at one side. These ridges may repre- 



