164 
ACTINOPTEETGJI. 
pterygopalatine arcade {pi.) bears at least one series of large, well¬ 
spaced conical or styliform teeth; and there is a cluster of similar 
teeth on the vomer ( vo .). The maxilla {moc.) is elongated, tapering 
in front; and the premaxilla {pmoc.) is very short, with a slender 
ascending process. The mandible is much deepened in the coronoid 
region, and von Zittel recognizes dentary (cZ.), splenial {spl.), and 
angular ( ar .) elements. In the hyoid arch, the epihyal, cerato- 
hyal, and hypohyal bones are well ossified. The opercular apparatus 
is complete; the suboperculum ( s.op .) exhibiting an ascending 
process at its antero-superior angle, and the large inferior limb of 
the preoperculum {p).op.) being much turned forwards. The bran- 
chiostegal rays ( hr .) are few, well-spaced, constricted at their point 
of attachment and much expanded in their distal portion. A gular 
plate has only been observed in Ophiopsis and Eusemius. 
The ossifications in the notochordal sheath do not advance beyond 
the stage of unconstricted rings; and Vetter 1 has observed completed 
annular pleurocentra and hypocentra alternating in the caudal 
region of Ophiopsis . The ribs are ossified, though usually delicate 
and not extending quite to the ventral border of the fish; and the 
neural spines are fused with their supporting arches both in the 
abdominal and caudal regions. 
The basals in the pectoral fin of Ophiopsis are not less than nine 
in number (PI. III. fig. 3) ; and the pelvic fin-supports are 
irregularly hour-glass shaped, the proximal end exhibiting the 
widest expansion. 
There is one series of enlarged postclavicular scales, especially 
well shown in Histionotus; and the dorsal fin-rays in this genus 
seem to be equal in number to the vertical series of regular flank- 
scales beneath them 2 . There are enlarged ridge-scales on the 
caudal pedicle, which attain an extreme development on its ventral 
border in Maevosemius. 
Synopsis of Genera. 
I..Dorsal fin single. 
Back nearly straight and dorsal fin occupy¬ 
ing from one-half to two-thirds of its 
length; caudal fin forked; fulcra on all 
median fins ; squamation complete and 
flank-scales scarcely if at all deepened.. Ophiopsis (p. 165). 
1 Mitth. k. mineral.-geol. Mus. Dresden, pt. iv. (1881), p. 56. 
2 See figure of Histionotus angularis by J. C. Mansel-Pleydell, Geol. Mag. 
[3] vol. vi. (1889), pi. vii. 
