GALLERY.] 
NATURAL HISTORY. (Fossils.) 
73 
by Sir Roderick I. Murchison. The remains in question are placed 
on the top of Case 3. Another very large species is the Holopty- 
chius Hibberti , from the carboniferous formation at Burdie House, 
near Edinburgh; and the specimen of Holoptychius Nobilissimus 
(in Case 3) discovered in the old red sandstone of Clashbinnie, 
near Perth, by the Rev. James Noble, is a very instructive example 
of the family, being one of the most perfectly preserved speci¬ 
mens. 
Case 7 is devoted to the species of the third family of the order, 
viz., the Dipterines—fishes with a heterocercal tail; with tolerably 
large rhomboidal scales, and provided with two dorsal as well as two 
anal, fins. They are from the old red sandstone and coal measures, 
and the specimens exhibited are chiefly from Scotland. 
The small family which follows—the Acanthodians, forms a group, 
the species of which, like the preceding, are from the Devonian rocks. 
It is represented in Case 8 by the genera Acanthodes , Diplacan- 
thus, Cheiracanthus, and Cheirolepis. The species have all of them 
remarkably minute scales; the head is large, the body rather short and 
tapering, and terminating by a heterocercal tail. In three of the 
genera there is but one dorsal fin, but in Diplacanthus there are two 
of these fins. Most of the species have the fins in question sup¬ 
ported in front by a spine. 
In the lower part of the Case are arranged the genera Pygopterus 
and Acrolepis. from the copper-slate of Mansfeld, Thuringia. They 
form part of the great family of the Sauroids, which occupies Cases 
9 to 12 inclusive. 
The Sauroid division contains species which exhibit both the hete¬ 
rocercal and the homocercal structure of tail, and are divided accord¬ 
ingly into two minor groups: they have conical teeth mixed with 
minute prickly teeth. The scales vary considerably in form. This 
family presents living examples in the Bony Pikes ( Lepidosteus ) of 
the rivers and lakes of North America, and a nearly allied fish ( Po- 
lypterus ) found in the Nile; and, in fossil species, it is represented in 
nearly all geological strata down to the Devonian period. 
The Lepidoids occupy the Cases 13 to 20. They have the same 
rhomboidal, enamelled scales as the Bony Pikes, but in general form 
they are usually shorter, and have a greater vertical diameter than 
the Sauroids: their jaws are provided with numerous teeth, which 
are more or less conical, but somewhat blunt. Very well pre¬ 
served specimens of the family will be seen in Cases 18 and 19 
among the species of JLepidotus, Dapedius , and Tetragonolepis , 
which are from the lias and oolitic formations. Some of the mem¬ 
bers of this division are found in the Devonian rocks, whilst, on the 
other hand, they are known to occur also in the lower tertiary beds, 
but no living species has been discovered. 
As in the preceding family, the Lepidoidei are some of them hete¬ 
rocercal, and some homocercal. 
The last family of the fishes with ganoid scales is the Pycnodonts, 
of which all the principal genera will be found in Cases 21 and 
22; and, arranged with the more or less perfect specimens of the 
fishes, will be found the isolated teeth, which, in their form and struc¬ 
ture, are very remarkable in this division. They are often rounded, 
