30 
B. Ganoids, in which the dorsal and haemal interspinous bones are equal in number 
to the opposed dermal fin-rays. 
Fam. Char. — Body fusiform or deep, with enamelled rhombic scales ; 
liead with well-developed membrane-hones, externally enamelled ; mouth 
small, and teeth conical or styliform. Upper lobe of tail very slightly 
produced. Bin-fulcra usually prominent. 
SEMIONOTUS, Agassh, 1813. 
Semionotus, Agassiz, Ecch. Poiss. Poss., IS43, A^oL ii, Pt. i, p. 222. 
Iscln/ptcnis, Egerton, Qufirt. Journ. Geol. Soc., 1817, A’^ol. iii, 1817, p. 277. 
Gen. Char. — Body elegantly fusiform; scales of the flank not more 
than twice as deep as broad, those of the ventral aspect equilateral or broader 
than deep ; dorsal ridge-scales present, but no ventral series. Teeth small, 
conical, and somewhat spaced. Paired fins moderately developed ; dorsal tin 
very large, arising near the middle of tlic back and partly opposed to the 
small anal ; caudal fin large, scarcely forked. Bulcra prominent upon all 
the fins. 
Ohs. — The scientific definition of this genus has only become jirecisc 
through the gradual progress of research since Agassiz’s original description. 
Bor, as pointed out by Prof. Oscar Braas,* the type-species, S. leptocephaliis, 
does not pertain to the same genus as the best preserved of the other 
specimens described under the name oi Semionotus ; and it appears certain 
that the original example of the species just mentioned belongs to the genus 
FhoUdop]iorus.-\ The second Agassizian species, S. Bergeri, is thus commoidy 
regarded as the type ; and tlic American Triassic fishes, named Ischypterus by 
Egerton, only differ from this form in the slightly greater devclojiment of the 
fin-fulcra — a feature of not more than specific value. 
The genus is essentially characteristic of early Mesozoic times — notably 
of the Trias and Ehintic ; and most of the species assigned to Semiouotus 
from tlie Lias and later deposits are erroneously determined. 
* 0. Fraas, “Ueber Seviionotus,” Wiirtt. .Taliresb., 1861, Vol. xvii, ]i. 85. 
t Smith Woodward, “Vertebrate Palaeontology in some Continental Museums,” Geol. Mag. [.S] 1888, Vol. v, 
p. 401. 
