MI ALL : BONES OF CTENODUS. 
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I have had by me are inferior in beauty and completeness to that 
figured by Mr. Atthey, which, however, it seemed needless to 
draw again. 
Operculum. The operculum in Ctenodus was probably com- 
posed of a single plate ; at least I have seen no trace of a second 
Fig. 7. — Ctenodus. Opercular. A, C. obliquus. B. G. elegans. x 
opercular bone. Both the outer and inner surfaces are exposed in 
different specimens, and one fine example, belonging to the Atthey 
collection, is clear on all sides. On the inner face there is a shallow 
depression towards the lower border of the bone ; this border is 
stouter than the other, and generally shows a blunt process. The 
examples figured are one of medium size, (C. obliquus ?) and one 
of small size, (C. elegans.) 
Vertebral Column. Vertebral centra, discoidal, of small antero- 
posterior thickness in proportion to their width, and pierced b}^ 
central apertures indicating the incomplete ossification of the 
notochord, often accompany unmistakeable remains of Ctenodus. 
Hancock and Atthey have described processes, which in one 
