PISCES.
The Fishes belonging to this division are at once recognised by the stiff spines which con stitute the first fin-rays of the dorsal fin, or which support the anterior fin of the back in case there are two dorsals. In some cases the an terior dorsal fin is only represented by detached spines. The first rays of the anal fin are like wise spinous as vvell as the first ray of the ven tral fin. This order, which comprises by far the greater number of osseous Fishes, is divi sible into the following families.
1st Family.— PERCI Perca, _Libra; Lates, Centropomus, Grammistes, Aspro, Apo gon, Cheilodipterus, Pomaiomus, Ambassis, Lucio-Perca, Serranus, Plectropoma, Diacope, Ilksoprion, Acerina, Itypticus, Polyprion, Centropristis, Grates, Cirrhites, Chironemus, Pomotis, Centrarchus, Priacanihus, Duks, Therapon, Pelates, &totes, Trichodon, Sillago, Holocentruni, Myripristis, Trachichiys, Trachinus, Percis, Pinguipes,Percophis,Uran oscopus, Polynemus, Sphyrana, Paralepis, 2nd Family.—SCLEROGENID.E (hard cheeks). Trigla, Prionotes, Pcristedion, Dactylopterus, Cephalacanthes, Coitus, Bemitripterus, Ilemi lepidotus, Platycephalus, Seorpana, Picrois, Blepsias, Apistes, Agriopes, Pelors, Synanceia, illonocentris, Gasterosteus, Oreosoma.
3d Family.— SCIEN ID/E. Sciana, EqUeS, Hamulon, Pristipoma, Diagramma, Lobotes, Cheilodactyles, Scolopsides, illicropterus, Am phiprion, Premnas, Pomacentres, Dascyllus, Glyphisodon, Helloes.
4th l'amily.—SPARIDIE. Sargus, Chryso phris, Pagrus, Pagellus, Denies, Cantharus, Boops, Oblada.
516 Family.—Airemax. Mena, Solaris, Casio, Germs.
6th Family. — SQUAMM I PENNE& Chtacr As reg,ards the texture of their bones, Fishes may be divided into osseous, fibro-cartilaginous, and true cartilaginous.
The cartilaginous, otherwise called Chondrop terygii, and which by their entire skeleton, by their branchiw, the external border of which is fixed to the skin, and from which the water escapes through narrow and multiplied orifices, as well as by other details in their economy, are distin guished from other Fishes, have never true bones ; their skeleton consists internally of a semi transparent cartilage, which in Rays and Sharks is coated at its surface only with a layer of opaque and calcareous grains.
The Sturgeon and Chimwra have the bones of the spine as soft as those of the Chondropteryg-ii, but the first of these genera has in many of the bones of the head and shoulder, at least a layer at the surface, completely ossified.
Other Fishes differ widely from each other in the hardness of the parts of their skeleton, and the fibro-cartilaginous have from this circum stance been erroneously associated with the Chondropterygii. In these, however, the cal careous matter, that is to say, the phosphate of lime, is deposited by fibres and layers in the cartilage, which serves as a basis to their bones, as is the case with the most perfectly osseous Fishes. It is only less abundant, and conse quently the texture of the bone does not be come so hard or homogeneous.
It is very gratuitously that the skeleton of ordinary Fishes has been supposed to be more flexible, of a softer nature, and more ex tensible than in the superior classes of Verte bmta. Most Fishes have their bones as hard as or harder than other animals, and there are even some, in the texture of which neither pores nor fibres are distinguishable, and which appear homogeneous or even vitreous to the eye.
No Fish, either osseous or cartilaginous, has a medullary canal in its bones; but there are some, as the Trouts, in which the bony tissue is more or less penetrated with an oily fluid.
There are some Fishes in which, whilst the rest of the skeleton acquires great hardness, some parts remain always cartilaginous, as for example, the head of the Pike.