Syngnathus and Nerophis become more common as we proceed southwards; but the existence of Scleroderms and Plectognaths is indicated by single individuals only, stragglers from their southern home, and unable to establish themselves in a climate ungenial to them.
The Gadoids are accompanied by Myxine; and Branchiostoma may be found in all suitable localities.
2. The Mediterranean district is distinguished by a great variety of forms; yet, with the exception of a few genera established for single species, none of the forms can be considered peculiar to it; and even that small number of peculiar genera is more and more diminished as our knowledge of the distribution of fishes advances. Some genera are identical with those found on the western coasts of the Atlantic and in the West Indies; but a most remarkable and unexpected affinity obtains with another very distant fauna, viz. that of Japan. The number of genera common to the Mediterranean district and the Japanese coasts is larger than that of the genera common to the Mediterranean and the opposite American coasts.
The Chondropterygians found in the British district continue in the Mediterranean, their number being increased by Centrina, Spinax, Pteroplatea, and some species of Rhinobatus, a genus more numerously represented in the Tropics. Torpedo and Trygon are common.
The greatest variety belong to the Acanthopterygians, as will be seen from the following list:—Labrax; Anthias, Serranus, Polyprion, Apogon, Pomatomus, Pristipoma, Diagramma (an Indian genus with two Mediterranean species, and otherwise not represented in the Atlantic), Dentex, Mæna, Smaris; Mullus; Cantharus, Box, Scatharxs, Oblata, Sargus, Pagrus, Pagellus, Chrysophrys; Sebastes, Scorpæna; Hoplostethus, Beryx, Polymixia; Trigla, Lepidotrigla, Agonus, Peristethus; Trachinus, Uranoscopus; Umbrina, Sciæna; Sphyræna; Aphanopus, Lepidopus, Nesiarchus, Trichiurus, Thyrsites; Cubiceps; Zeus, Cyttus; Stromateus; Trachurus, Caranx, Capros, Diretmus, Antigonia; Callionymus; Batrachus; Lophius; Cristiceps, Tripterygium; Cepola; Lepadogaster; Centriscus; Notacanthus.
The Labridæ are as common as, or even more so than, in the British district, and represented by the same genera. But, besides, some other Pharyngognaths, properly belonging to the Tropical Atlantic, have fully established themselves, though only by a few species, viz. Glyphidodon and Heliastes; Cossyphus, Novacula, Julis, Coris, and Scarus.
The Gadoids show a marked decrease of development; and the species of Gadus, Gadiculus, Mora, Strinsia, Phycis, and Molva, which are peculiar to the Mediterranean, seem to inhabit rather the colder water of moderate depths, than the surface near the shore. Motella, however, proves to be a true Shore fish also in the Mediterranean, at least in its adult state. Ophidium and Fierasfer appear now besides Ammodytes. As the Gadoids decrease, so the Pleuronectidæ increase, the genera of the Mediterranean district being Rhombus, Phrynorhombus, Arnoglossus, Citharus, Rhomboidichthys, Pleuronectes (a northern genus not extending farther southwards), Solea, Synaptura, and Ammopleurops.
The variety of Physostomes is small; the following only being superadded to those of the British district:—Saurus (a tropical genus), Aulopus; Congromuræna, Heteroconger, Myrus, Ophichthys, Muræna.
The Lophobranchs are more numerous in species and individuals than in the British district; and, besides Syngnathus and Nerophis, several species of Hippocampus are common. Also a few species of Balistes occur.
Myxine is lost in this district; whilst Branchiostoma is abundant.