74 NATCJRAL HISTORY. (Fossils.) [NORTH 
and implanted in the jaw like the paving stones of the road, the crowns 
being but moderately convex: usually there are several rows in each 
jaw. The oblong and somewhat wedge-shaped masses containing 
several rows of teeth (a central row of larger, and lateral rows of 
smaller teeth), and these arranged symmetrically, form the palatal por¬ 
tion of the upper jaw. These teeth are admirably adapted for crush¬ 
ing shell fish, and, no doubt, such was the food of the Pycnodonts. 
They were of a short form, and the body was high and compressed; 
a large proportion of the species are from the Jurassic rocks; they 
occur also in the chalk, and in the tertiary formations, but none 
exist in the present seas. 
On the lower shelves of Case 22 are placed the genera of the 
small family of Scleroderms, a group which is very isolated in its 
characters. The remarkable genus Blochius is here represented by a 
fine specimen of B. longirostris, from the Eocene of Monte Bolca; 
and there is a fine series of the JDercetis from the chalk of Lewes. 
In the preceding two great divisions of fossil fishes, many of the 
families of which they are composed are extinct, and a very large pro¬ 
portion of the species are confined to the geological strata beneath the 
chalk, whilst those which now come under consideration belong en¬ 
tirely to the chalk and tertiary formations, and the families have 
living representatives. They constitute several important sections, 
though somewhat arbitrarily divided into Ctenoids and Cycloids. 
The species arranged in Cases 23 to 27 inclusive have the 
Ctenoid structure of scale, namely, a horny scale with the free edge 
serrated ; of this division the Perches may be regarded as typical. In 
Case 24 a fine fossil species, the Perea lepidota , from GBningen, 
may be noticed as forming a good example of the group. 
Among specimens of other genera belonging to the Percoids may be 
mentioned the fine series from the Sussex chalk, of Beryx ornatus 
(Case 23, upper shelves), which formed part of Dr. Manteli’s rich 
collection. 
Of the few fossil Sparoids , or Breams (Case 25, lower shelves), 
the Sparnodus macrophthalmus, from Monte Bolca, and the Scicenurus 
Bowerbankii, 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 26), 
the Goboids or Gobies, and the Teuthies of Cuvier, most of the fossil 
representatives of which families are from Monte Bolca. The Mu- 
gilidce (Case 26) is here represented by the Mugil princeps, from the 
tertiary formation of Aix, in Provence. 
Among the fossil species belonging to the family of the Chcetodons 
( Case 26, 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. 
The principal genus of the family of Aulostomes ( Case 26, lower 
shelves) is Fistularia, one species of which occurs at Monte Bolca; 
the other, Fistularia Konigii , Agass., in the slate of Engi, Canton 
Glaris. 
The fourth Order, the Cycloid Fishes, (so denominated from 
the circular form of the scales, consisting of corneous layers 
and having their posterior margin entire,) is represented by the 
