GALLERY.] NATURAL HISTORY. (Fossils.) 87 
The Pycnodons (Cases 15, 16, lower shelves). Several of the 
specimens here deposited are illustrative of the character by which the 
teeth of the fishes of this family may easily be distinguished from those 
of some placoid fishes. Among the largest of the teeth are those of some 
species of Pycnodon, from the upper oolite, especially P. Gigas , and of 
Sphcerodus Gigas, formerly described as petrified eyes of toads, &c.; also 
the teeth of Placodus Gigas, from the Muschelkalk of Franconia, 
deserve particular notice. 
The family of Scleroderms ( Cases 15 and 16, middle shelves): among 
the species belonging to it, in the collection, are: a suite of specimens 
of Dercetis elongatus, chiefly from the chalk of Preston, near Brighton ; 
the Acanthopleurus serratus , likewise from the chalk formation (slate 
of Glaris); and the Blochius longirostris, from Monte Bolca. 
The third Order of fishes, the Ctenoijjs, or Ctenolepidoti 
(so called from their scales being formed of layers, of which the upper¬ 
most are denticulated or comb-toothed at their posterior margin) is 
divided into the following families—the Percoids, Sparoids, Scienoids, 
Cottoids, Gobioids, Aulostomes, Chetodons, Pleuronects, and Mugil- 
loids. The type of the first of them (Cases 17 and 18) is the perch; 
and of the three fossil species known, the Perea lepidota from 
Oeningen, of which a remarkably perfect specimen is here deposited, is 
the largest. Among specimens of other genera belonging to the Per¬ 
coids may be mentioned the fine series from the Sussex chalk, of 
Peryx Lewesiensis, which (as also that of Dercetis, in this Case) formed 
part of Dr. Mantell’s rich collection; and three scarce species of 
Rhacolepis, placed with them, are from the chalk formation of Brasil. 
Of the few fossil Sparoids, or Breams, (Case 19,) the Sparnodus 
ovalis, from Monte Bolca, and the Scicenurus JBowerbankii , from 
Sheppey, may be mentioned: all the fishes of this family are from 
more recent formations than the chalk, as is also the case with the 
species of the Cottoids or Bullheads, (Case 19, middle,) the Goboids 
or Gobies, and the Teuthies of Cuvier, most of the fossil representa¬ 
tives of which families are from Monte Bolca. 
The principal genus of the family of Aulostomes, (Case 20, lower 
shelves,) is Fistularia, one species of w^hich occurs at Monte Bolca; 
the other, Fistularia magnijica (Egert. Catal.), in the Engi slate of 
Canton Glaris. 
Among the fossil species belonging to the family of the Chcetodons , 
(Case 20, middle,) all from Monte Bolca, and more recent tertiary form¬ 
ations, may be particularized the very perfect specimen (with counter¬ 
part) of that most singular fish, the Semiophorus velifer , from the above 
locality ; and a series of those well-known osseous bodies found in the 
crag of Norfolk, which, when cut and polished, have the appearance of 
marbled pebbles, but are recognized by Agassiz as interapophysal bones 
of a species of Platax called P. Woodwardi. 
The family of Pleuronects ( Case 20, middle) is represented by one 
genus only, namely Rhombus, having one fossil species, the elegant R. 
minimus, smaller than any of the recent species, from Monte Bolca: 
the specimen here preserved was presented, together with those of the 
Semiophorus, by Chambers Hall, Esq. 
The last family of this order, the Mugiloids, (Case 20, upper shelves,) 
to which belongs the genus Mugil } with only one species, M. princeps, 
