RHIZODOXTim®. 
341 
Family RHIZODONTIDiE. 
Body fusiform, robust, elongated, and somewhat depressed, with 
cycloidal scales, more or less deeply overlapping, exhibiting a 
rounded boss or short rib on the middle of the inner side, and 
sometimes covered externally with a thin layer or detached rugae 
of ganoine. Head and opercular apparatus with well-developed 
membrane-bones ; parietals large and separate, frontals separate, 
and orbits far forwards; interoperculum absent: jugular plates 
comprising one large pair, flanked on either side by a lateral series, 
and with a small azygous element in front. Dentary bone of man¬ 
dible thin and vertical, with well-developed infradentaries in the 
same plane; an inner series of a few large, narrow, shuttle-shaped 
bones, each supporting a “ laniary” tooth; a pair of similar teeth 
on the roof of the mouth, but the marginal upper dentition feeble. 
Teeth conical, with a pulp-cavity of which the walls are vertically 
folded towards the base. Pectoral and pelvic fins obtusely lobate; 
two remote dorsal fins, the first nearly opposite or directly opposed 
to the pelvic pair; anal fin single, caudal fin diphyeercal or 
heterocercal. 
Synopsis of Genera. 
I. Infraclavicle with long upwardly directed 
process. 
Teeth smooth, with a pair of sharp edges. 
Teeth rounded in section. 
II. Infraclavicle without an ascending pro¬ 
cess; dorsal fins directly opposed to 
pelvic and anal fins. 
Teeth rounded in section, smooth; ring- 
vertebrae : tail heterocercal, and cau¬ 
dal fin rhomboidal. . . 
No ring-vertebrae; tail almost diphvcercal, 
and caudal fin rhomboidal . 
Teeth rounded in section ; ring-vertebrae ; 
tail almost diphyeercal and truncated. 
Teeth compressed, with a pair of sharp 
edges ; ring-vertebrae ; tail hetero¬ 
cercal and truncated. 
Rhizodus (p. 342). 
Strepsodus (p. 348). 
Rhizodopsis (p. 354). 
GyroptycMus (p. 358). 
Tnsticliopterns (p. 360). 
Eusthenopteron (p. 361). 
