OF THE EARLIER VERTEBRATA. 



49 



mens indicate the nasal openings a little in advance of the 

 eyes. The nape of the creature was covered by three de- 

 tached plates (9, 9, 9, fig. 13), which rested upon anterior 

 dorsal scales, and whose homologues, in the osseous fishes, may 

 possibly be found in those bones which, uniting the shoulder- 

 Fig 13. 



UPPER PART OF HEAD OF OSTEOLEPIS. 



bones to the head, complete the scapular belt or ring. The 

 operculum we find represented by a single plate (8), which 

 had attached to it, as its sub-operculum, a plate (13) of nearly 

 equal size (see figs. 14 and 15.) Four small plates (2, 4, 5) 

 formed the under curve of the eyes, described in many of the 

 osseous fishes by a chain of small bones or ossicles; a consi- 

 derably larger plate (6) occupied the place of the pre-opercu- 

 lar bone ; while the intermaxillaries bad their representatives 

 in well-marked plates (3, 3), which, in the genera Osteolepis, 

 Diplopterus, and Glyptolepis^ we find bristling so thickly with 

 teeth along their lower edges, as to remind us of the minia- 

 ture saws employed by the joiner in cutting out circular holes. 

 These external intermaxillaries did not, as in the perch or cod, 

 meet in front of the nasal bone and vomer, but joined on at 

 the side, a little in advance of the eyes, leaving the rounded 



