MACR0SEMIID2E. 
165 
Back elevated and angulated anteriorly, the 
dorsal fin extending from the angula¬ 
tion almost to the caudal fin, which is 
deeply forked; uniserial fulcra on both 
paired and median fins; squamation 
complete and flank-scales deepened .. 
Back nearly straight, and dorsal fin extend¬ 
ing almost its whole length ; squama¬ 
tion apparently complete, the flank- 
scales very large and much deepened.. 
Back nearly straight, and dorsal fin extend¬ 
ing almost its whole length; caudal fin 
not forked, rounded; fulcra only on the 
caudal fin; scales thin, wanting dorsally 
and ventrally, those of the flank scarcely 
deepened and the vertical series dicho¬ 
tomous above; much-enlarged ridge- 
scales on lower border of caudal pedicle. 
Back nearly straight, and dorsal fin extend¬ 
ing almost its whole length ; (P) no anal 
fin; squamation robust and complete, 
but irregular, the flank-scales not much 
if at all deepened, the vertical series 
apparently sometimes dichotomous 
dorsally and ventrally . 
II. Dorsal fin subdivided into two parts. 
Vertebral rings feeble or absent; anterior 
portion of dorsal deeper than the pos¬ 
terior portion ; squamation complete . . 
Vertebral rings robust; anterior portion of 
dorsal with comparatively widely spaced 
rays, not deeper than the posterior por¬ 
tion ; squamation complete. 
Histionotus (p. 173). 
Legnonotus (p. 176). 
Macrosemius (p. 176). 
Petalopteryx (p. 181). 
Propterus (p. 183). 
Notagogus (p. 186). 
Genus OPMIOPSIS, Agassiz. 
[Neues Jahrb. 1834, p. 385.] 
Trunk much elongated, gradually tapering from the occiput back¬ 
wards or the dorsal margin only slightly arcuate ; head large or of 
moderate size. Marginal teeth acutely pointed. Notochord invested 
with delicate ring-vertebrae ; ribs ossified. Bifurcation of dorsal 
fin-rays variable ; fulcra often absent on paired fins and usually 
confined to the base of the median fins. Paired fins relatively 
large; dorsal fin ordinarily extending about half the length of the 
back, high in front, low behind; anal fin small; caudal fin forked. 
Scales covering the whole of the trunk, in regular series, united by 
