PLATE XX XoVALT: 
ONYCHODUS SIGMOIDES, Newb. (p.56). 
Fies. 1, 2. Jugular plates. 
3. Entire frontal plate. 
4, Anterior half of two frontals, in position. 
5. Supra-temporal plate. 
6. Operculum, inside. 
7. Clavicle, inside. 
. 8. Parietal ? , inside. 
9. Suboperculum ?, outside. 
10. Suboperculum ?, inside. 
11. Operculum of small individual, outside. 
All figures, except 1], half natural size. 
Corniferous limestone, Delaware, Ohio. 
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