Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/697

679 JARINE FISHES.] ICHTHYOLOGY 079 Phrynorhomlus, Plcuronectes, Solea, and only the fiist two are not met with in the Mediterranean. Labroids are common ; with the exception of the North American Tautoga, all the other genera are met with. Physostomes are not well represented, viz., by one species of Osmcnts, one of Engraulis, one of Conger, and about five of Clupca. Syngiiathiis and Nerophis become more common as we proceed southwards ; but the existence of Scleroderms and Plectognatha is indicated by single individuals only, stragglers from their south ern home, 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, Ptcroplatea, and some species of Rhinobatus, a genus more numerously represented in the tropics. Toledo and Trygon are common. The greatest variety belong to the Acanthopterygians, which are represented by fifty-seven genera. The Labridce are as common as in the British district, or even more so, and are represented by the same genera. But, besides these, 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 Scams. The Gadoids show a marked decrease of development ; and the species of Gadus, Gadiculus, Mora, Strinsia, Phycis, and Moha 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 also to be a true shore fish in the Mediter ranean, at least in its adult state. Opliidium and Ficrasfer appear now besides Ammodytes, As the Gadoids decrease, so the Pleuro- neciidni increase, 9 genera being found in this district. The variety of Physostomes is small, the following only having to be added to those of the British district : Saurus (a tropical genus), Aulopus ; Congromurccna, Heteroconger, Myrus, Ophichthys, MurcRna. 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. A few species of Bnlistcs also occur. Myxine is lost in this district, whilst Branchiostoma, is abundant. 3. The shore fishes of the North American district consist, as on the eastern coasts of the North Atlantic, of northern (about 50 general and southern (about 30) elements ; but they are still more mixed with each other than on the European coasts, so that a boundary line cannot be drawn between them. The affinity to the fauna c.f the eastern shores is great, but almost entirely limited to the genera composing the fauna of the British district. British genera not found on the American coasts are Galeus, Scyllium, Chimcera, ifullus, Pagellus, Trigla, Trachinus, Zeus, Callionymus. The southern elements of North America are rather derived from the West Indies, and have no special affinity to Mediterranean forms ; very few of the non-British Mediterranean forms extend across the Atlantic ; instead of a Mediterranean we find a West Indian element. Many of the British species range across the Atlantic, and inhabit in an unchanged condition the northern parts of this district ; and from the frequent occurrence of isolated specimens of other British species on the North American coast, we may presume that many more occasionally cross the Atlantic, but without being able to obtain a permanent footing. The genera peculiar to this district are few in number, and com posed of very few species, viz. , Hemitriptcrus. Pammclas, Chasmades, Cryptucantlwdcs, and Tautoga. Temperate North Pacific. This fauna shows a great affinity to that of the Temperate North Atlantic, not only in including a considerable proportion of identical genera, and even of species, but also in having its constituent parts similarly distributed. Our knowledge of the ichthyology of this fauna, however, is by no means complete, and the details of the distribution of the fishes of these shores have still to be worked out ; nevertheless, three divisions may be recognized which, for the present, may be defined as fol lows : 1. The fishes of the north-western shores, to about 37 N. lat., including the corresponding northern parts of Japan : Kamtchatkan district. This corresponds to the British district of the Atlantic. * 2. The fishes of southern Japan and the corresponding shores of the continent of Asia, between 37 and 30 6 N. lat. : Japanese district, which corresponds to the Medi terranean. 3. The fishes of the eastern shores southwards to the latitude of San Francisco : Californian district. This corre sponds to the North American district of the Atlantic. Too little is known of the shore fishes of the coasts be tween San Francisco and the tropic to enable us to treat of it as a separate division. The shore fishes of the North Pacific generally are com posed of the following elements : a. Arctic forms which extend into the Arctic Ocean, and the majority of which are also found in the British district. b. Peculiar forms limited to the North Pacific, like the Heterolepidina, Embiotocidce, and certain Cottoid and Blen- nioid genera. c. Forms identical with fishes of the Mediterranean. d. Peculiar forms limited to the southern parts of Japan. e. Tropical forms which have entered the North Pacific from the south. 1. To the Kamtchatkan district we can assign but a small list of fishes, probably because of the imperfect manner in which its fauna has been explored. At present we have positive knowledge of the occurrence of only two Chondropterygians, viz., Chimcera and Raia; the species of the latter genus seem to be much less numerous than in the Atlantic. Of Acanthopterygians 15 genera are known. Labroids are absent ; they are clearly a type unable to endure great cold ; of the Embiotocoids which represent them in the Pacific, one species only (a species of Ditrema) is known from this district. The Gadoids are, so fur as we know at present, sparsely repre sented, viz. , by isolated species of Gadus, Motella, and Lot el la, the last being an inhabitant of moderate depths rather than of the surface. Hippoglossus, Plcuronectes, and Parophrys seem to occur everywhere in suitable localities. The Physostomes are nearly the same as in the British district, viz., a smelt (Hypomesus], probably also the arctic Mallotus, an anchovy, several species of Clupea, and the conger-eel. A very singular Salmonoid fish, Salanx, which is limited to the north western Pacific, occurs in great abundance. The Lophobranchs also correspond in their development to those of the British district, Nerophis being replaced by Urocampus. Neither Myxinoids nor Branchiostoma have as yet been found. 2. The Japanese district is, like the Mediterranean, distinguished by a great variety of forms. Of 102 genera known to inhabit these coasts, 13 are peculiar to it, 53 occur in the Mediterranean, though also in other districts. This resemblance to the Mediterranean is even greater than would appear from a comparison of the genera, inasmuch as a considerable number of species are identical in both districts. Three of the Berycoid genera have hitherto been found in the Japanese and Mediterranean districts and nowhere else. Another very singular fact is that some of the most characteristic genera, like Mullus, Zeus, Callionymus, Ccntriscus, inhabit the Mediterranean and Japanese districts, but have never reached the op posite American coasts, either in the Atlantic or the Pacific; although, at least in the latter, the oceanic currents would rather favour than obstruct their dispersal in the direction of America. Bold as the hypothesis may appear, we can only account for the singular dis tribution of these shore fishes by assuming that the Mediterranean and Japanese seas were in direct and open communication with each other within the period of the existence of the present Teleosteous fauna. Gadoids have disappeared, or are represented by forms inhabiting moderate depths. Neither Myxine nor Branchiostoma are as yet known to have been found. 3. The Californian district includes a marked northern element, the principal constituents of which are identical with types occurring in the corresponding district of the Atlantic, viz., the North American, as exemplified by Discoboli, Anarrhichas, Ccntronotus, Coitus, Hippoglnsxus, Chipra (harengtts), &c. But it possesses also, in the greatest degree of development, some types almost peculiar to itself, as the Heterolepidina, some remarkable Cottoid and Blennioid genera, and more especially the Embiotocoids viviparous Pharyngognaths which replace the Labroids of the other hemi-