680 ICHTHYOLOGY [DISTRIBUTION. sphere. Gadoids are mneliless numerous than in the North Ameri can district. The southern forms are but little known, but it may be anticipated that, owing to the partial identity of the faunae of the two coasts of the isthmus of Panama, a fair proportion of West Indian forms will be found to have entered this district from the south. EQUATORIAL ZONE. As we approach the tropic from the north, the types characteristic of the arctic and tem perate zones become rarer, and disappear altogether, to be replaced by the greater variety of tropical types. Of Chondropterygians, the Ckima-ridce, Spinacidce, Mustelus, and Raia do not pass the tropic, or appear in single species only; and of Teleosteans, the Berycida>, Pagrus, iheHetero- lepidina, Coitus and allied genera, Lophius, Anarrhichas, Stickceus, Lepadogaster, Psychrolutes, Centriscus, Notacan- ihus, the Labridve and JEmbiotocidce, the Lycodklce, Gadidae, and marine Salrnonidce either entirely disappear, or retire from the shores and surface into the depths of the ocean. With regard to variety of forms, as well as to number of Individuals, this zone far surpasses either of the temperate zones ; in this respect, the life in the sea is like that on the land. Shore fishes are not confined to the actual coast line, but abound on the coral reefs with which some parts of the Atlantic find Pacific are studded, and many of which are below the surface of the water. The abundance of animal and vegetable life which flourishes on these renders them the favourite pasture grounds for the endless vaiioty of coral- fishes (Sguamipinnes, Acronuridce, Pomacentridce, Jnlidce, Plectognathi, &c.) and for the larger predatory kinds. The colours and grotesque forms of the fishes of the tropics justly excited the admiration of the earliest observers. Scarlet, black, blue, pink, red, yellow, &c., are arranged in patterns of the most bizarre fashb, mingling in spots, lines, or bands, and reminding us of the words of Captain Cook when describing the coral-reefs of Palmerston Island: " The glowing appearance of the mollusks was still inferior to that of the multitude of fishes that glided gently along, seeuungly with the most perfect security. The colours of the different sorts were the most beautiful that can be imagined the yellow, blue, red, black, &c., far exceeding anything that art can produce. Their various forms, also, contributed to increase the richness of this submarine grotto, which could not be surveyed without a pleasing transport. " Of Chondropterygians the Scylliidce, Pristis (saw-fishes), Rhinobatidae, and Trygonidce attain to the greatest develop ment. Of Acanthopterygians C entropristis, Serranus, Pledropoma, Mesoprion, Priacanthus, Apogon, Pristipoma, llcenulon, Diayramma, Gerres, Sco^sis, Synagris, Ctesio, Mullidce, Lethrinus, Squamipinnes, Cirrhites, some genera of Scorpcenidte, Platycephalus, Scitenidce, Sphyrcena, Caranx, Eqttula, Callionynms, Teuthis, Acanthurus, Na- sctis, are represented by numerous species ; and the majority of these genera and families are limited to this zone. Of Pharyngognaths the Pomaceutridce, Julidina, and Scarina are met with near every coral formation in a living con dition. Of Gadoids, a singular minute form, Bregmaceros, is almost the only representative, the other forms belonging to deep water, and rarely ascending to the surface. Flat fishes (Pleuronectidce) are common on sandy coasts, and the majority of the genera are peculiar to the tropics. Of P/iysostomi only the Saurina, Clupeidce, and Murcenidce are represented, the Clupeidae being exceedingly numerous in individuals, whilst the Murcenidce live more isolated, but show a still greater variety of species Loplwbrancltii and Sderodermi are generally distributed Branchiostoma has been found on several coasts. Geographically it is convenient to describe the coast fauna of the tropical Atlantic separately from that of the Indo-Pacific Ocein. The differences between them, how ever, are far less numerous and important than between the- freshwater or terrestrial faunae of continental regions. The majority of the principal types are found in both, many of the species being even identical; but the species are far more abundant in the Indo-Pacific than in the Atlantic, owing to the greater extent of the archipelagoes in the former. But for the broken and varied character of the coasts of the West Indies, the shores of the tropical Atlantic would, by their general uniformity, afford but a limited variety of conditions for the development of specific and generic forms, whereas the deep inlets of the Indian Ocean, with the varying configuration of their coasts and the different nature of the bottom, its long peninsulas, and its archipelagoes, and the scattered islands of the tropical Pacific, render this part of the globe the most per fect for the development of fish life. The fishes of the Indian and Pacific Oceans (between the tropics) are almost identical, and the number of species ranging from the Red Sea and the east coast of Africa to Polynesia, even to its most westerly islands, is very great indeed. This Indo-Pacific fauna, however, does not reach the Pacific coast of South America. The wide space devoid of islands east of the Sandwich Islands and the Marquesas group, together with the current of cold water which svvaeps northwards along the South American coast, has proved to be a very effectual barrier to the eastward extension of the Indo-Pacific fauna of coast fishes ; and, consequently, we find an assemblage of fishes on the American coast and at the Galapagos Islands, sufficiently marked to constitute a distinct zoologi cal division. Tropical Atlantic. The boundaries of the tropical Atlantic extend zoologically a few degrees beyond the northern and southern tropics, but, as the mixture with the types of the temperate zone is very gradual, no distinct boundary line can be drawn between the tropical and tem perate faunae. Types almost exclusively limited to it and not found in the Indo-Pacific are few in number, as Centropristis, Rhypticus, llcwmdon, Mcdthe. A few others preponderate with regard to the number of species, as Pledropoma, Sargus, I rachynotus, Batrachidce, and Gobiesocidce. The Scia^noids are equally represented in both oceans. All the remainder are found in both, but are in a minority in the Atlantic, where they are sometimes represented by one or two species only (for instance, Lethrinus). Tropical Indo-Pacific Ocean. The ichthyological boun daries of this part of the tropical zone may be approxi mately given at 30 D N. and S. lat. ; on the Australian coasts it should probably be placed still farther south, viz., at 34 ; it includes, as mentioned above, the Sandwich Islands, and all the islands of the South Sea, but not the American coasts. Some eighty genera of shore fishes are peculiar to the Indo-Pacific, but the greater number consist of one or a few species only ; comparatively few have a plurality of species, as Diagramma, Lethrinus, Eqvida, Teuthis, Ampliiprion, Dascyllus, Choerops, Chilinus, Anampses, Stethqjulis, Coris, Coilia. The sea-perches, large and small, which feed on crusta ceans and on other small fishes, and the coral -feeding Pharyn gognaths, are the types which show the greatest generic and specific variety in the Indo-Pacific. Then follow the Squamipinnes arid Murcenidce, the Clupeidce and Co/ran- fjidx, families in which the variety is more that of species than of genus. The Scoiycenidce, Pleuronectidce, Aero- nuridoe, Scicenidce, Syngnatkidce, and Teuthyes are those which contribute the next largest contingents. Of shore- loving Chondroptery^ans the Scylliidce and Trygonida only are represented in moderate numbers, though they are more numerous in this ocean than in any other.
Pacific Coasts of Tropical America. As boundaries
