108 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 
Genus—ACROLEPIS, Agassiz, 1833. 
? GyroLerpts, Agassiz (pars). 
Patzoniscus, G. A. Kurtze (pars). 
Patmoniscus, EH. F. Germar (pars). 
Hotoprycuivs, M‘Coy (pars). 
AmBLYPTERUS, A. Fritsch (pars), afterwards corrected. 
? Exonicuruys, A. S. Woodward (pars). 
Eronicuruys, Traquair (pars). 
Generic Characters.—Fusiform or elongated ; suspensorium oblique, gape wide ; 
teeth sharply conical, of two principal sizes, a set of larger ones situated internally to a 
wore numerous and closely placed set of smaller ones. Head-plates ornamented with 
ridges or tubercles which may pass into each other. Scales thick, with extensive covered 
area (PI. XXV, figs. 2—4, 9—11) which is frequently produced upwards into a pointed 
process ; articular peg and socket strongly developed in the flank-scales. Ornament of 
exposed arev of scales normally consisting of prominent ridges passing obliquely across 
the surface, but which may coalesce at places so as to produce a reticulated or even pitted 
appearance. Posterior edges of scales in most species entire and undenticulated. 
Principal rays of pectoral fin unarticulated for about one third of their length; base of 
ventral not extended ; dorsal placed nearly opposite the interval between the ventrals and 
the anal; dorsal and anal triangular-acuminate in shape; caudal powerfully heterocercal 
and deeply cleft. Fin fulera distinct but small. 
Observations. —On the whole Acrolepis resembles Hlonichthys pretty closely, though 
it is also very decidedly separated by the deeply imbricating arrangement of the scales 
with concomitant greater breadth of the overlapped area. As remarked above, the 
posterior margins of the scales are in most cases not denticulated ; an exception seems, 
however, to occur in an African species from the Karoo formation named by Smith 
Woodward Acrolepis (?) digitata, in which “the hinder border exhibits a series of very 
large downwardly directed denticulations,’—it must, however, be remembered that he 
himself states that the name is a provisional one.’ I have recently seen reason to transfer 
my Acrolepis (2?) Africana from Nyassaland, in which the posterior margin of the scales 
is also denticulated, to the genus Colobodus of Agassiz. Nevertheless the presence of 
denticulations on the posterior borders of the scales seems after all to be only of specific 
value. For although this character, for example, is found pretty constantly throughout 
the genus Rhadinichthys, yet in at least two species referable thereto—Rd. Macconochit, 
Traq. and Rh. tuberculatus, Traq., to be presently described, the posterior margin in all 
the scales is quite plain. 
In Pl. XXYV, fig. 1, we have an outline sketch of the maxilla and mandible of the 
1 «Cat. Foss. Fishes Brit. Mus.,’ pt. ii, 1891, p. 508. 
