562 
DE. A. GUNTHER’S DESCRIPTION OE CEEATODUS. 
PLATE XXXI. 
Structure of the Scales. 
Pig. 1. A scale taken from the lateral line of Ceratodus forsteri, outer surface. Natural 
size. 
Fig. 2. Inner surface of the same scale. 
Fig. 3. One half of a vertical transverse section across the middle of the scale, magn. 8. 
The vertical divisions ( a , a) indicate the place where the section passed 
through the sutures dividing the outer surface into trapezes. 
Fig. 4. A portion of the same section, magn. 216. 
a. A layer of fibres cut transversely. 
h. A layer of fibres cut obliquely. 
c. A layer of fibres cut longitudinally. 
d. Outer calcified stratum. 
Fig. 5. Three layers of fibres crossing each other at angles of 90° or 45°, magn. 216. 
Figs. 6-8. Portions of the calcareous stratum, after removal of the organic matter by 
burning, magn. 216: 6, from the middle of the lateral area of the scale; 
7, from the exposed area; 8, from the posterior area. 
Fig. 9. Eight upper tooth of Ceratodus forsteri, nat. size. 
Fig. 10. Eight upper tooth of Ceratodus runcinatus, from the Muschelkalk, nat. size. 
From a specimen in the British Museum. 
PLATE XXXII. 
Microscopical Structure of the Teeth , compared with that in Fossil species , Protopterus 
and Psammodus. 
Fig. 1. Front part of one half of the lower jaw, with a vertical section through the tooth 
(nat. size). 
a. Dentine. 
h. Pulp-cavity. 
c. Osseous base of tooth. 
d. Dentary bone. 
e. Cartilaginous symphysis. 
Fig. 2. The same section through the lower tooth, magnified : the clear vertical line indi- 
cates that a portion of the length of the tooth is left out. 
a. Dentine with medullary canals. 
1). Pulp-cavity. 
c. Spongious osseous base of the tooth. 
Fig. 3. Vertical section through the front prong of the lower tooth of Protopterus , 
magn. 20. 
a. Spongious osseous base of tooth. 
b. Pulp-cavity. 
