7 
simply adopt the term for convenience, an^aiting the further development 
of palaeontological research to confirm or modify the apparently now reason- 
able classification of Coj)e.* 
The subdivisions of the Ganoids are still equally under dispute, and it 
will suffice for the present Memoir, which deals only wifh actinopteran 
families (/.<?., those in which the paired fins are non-lofiate), to distinguish 
between that type in which the interspinous hones of the median fins are 
fewer in number than the apposed dermal fin-rays, and the more specialized 
type in which cacfi fin-ray has a separate support. As remarked, esjiecially 
by Cope,t the stages presented by the development of the appendicular 
skeleton, are of great taxonomic significance ; and it may now he regarded 
as proved, that the “ crossopterygian” limb and the non-correspondence of the 
ends and exo-skeleton in the median fins are marks of inferiority of generaliza- 
tion. The heterocercal tail likewise persists in many eases untilt he “ actinop- 
teran” limb has lieen developed (Pala^oniscidai) ; hut as soon as there is a 
tendency towards the correlation of the interspinous l)ones and the median 
fin-rays, the upper lobe gradually atropiiies and externally disappears. 
A —Ganoids in which the dorsal and haemal interspinous bones are less numerous 
than the apposed dermal fin-rays. 
(i).— Caudal fin heterocercal. 
Farniltf-YALmomsClDM. 
Fam. Char . — Body elongate, fusiform ; scales, when present, rhombic 
(rarely in part cycloidal), enamelled; dorsal fin rarely remote. Head-hones 
well-developed, externally enamelled ; eye far f oru ards, and snout prominent ; 
mandibular suspensorium more or less obli(|uc, and the mouth deeply cleft. 
A series of l)road l)ranchiostegal rays, the most anterior pair especially large, 
with a small median element. 
MYllIOLEPIS, Egerton, 1861. 
(Quart. .Journ. Geol. Soc., Vol. xx, p. 3.) 
Gen. Char . — Head large, snout obtuse ; suspensorium oblique ; gape 
very wide, with the teeth large and conical ; fins well-developed, the dorsal 
high and triangular in form, placed opposite the S 2 )ace between the j)elvis 
* E. D. Cope, “ Observations on the Systematic Relations of the Fishes,” Proc. Amer. Assoc. Aclv. Sci., 
1871, p. 326. 
t E. D. Cope, Review in Amer. Xaturalist, 1887, p. 1015. 
