The _fresh-water Perches_ of Europe and of the North of America are represented in Ceylon and India by several genera, which bear to them a great external similarity (_Lates, Therapon_). They have the same habits as their European allies, and their flesh is considered equally wholesome, but they appear to enter salt-water, or at least brackish water, more freely. It is, however, in their internal organisation that they differ most from the perches of Europe; their skeletons are composed of fewer vertebræ, and the air bladder of the _Therapon_ is divided into two portions, as in the carps. Four species at least of this genus inhabit the lakes and rivers of Ceylon, and one of them, of which a figure is given above, has been but imperfectly described in any ichthyological work[1]; it attains to the length of seven inches. [Footnote 1: Holocentrus quadrilineatus, _Bloch_. It is allied to _Helotes polytoenia_, Bleek., from Halmaheira which it can be readily distinguished by having only five or six blackish longitudinal bands, the black humeral spot being between the first and second; another blackish blotch is in the spinous dorsal fin. There are two specimens in the British Museum collection, one of which has recently arrived from Amoy; of the other the locality is unknown. See GÜNTHER, _Acanthopt. Fishes_, vol. i. p. 282, where mention of the black humeral spot has been omitted.] [Illustration: THERAPON QUADRILINEATUS.] In addition to marine eels, in which the Indian coasts abound, Ceylon has some true fresh-water eels, which never enter the sea. These are known to the natives under the name of _Theliya_, and to naturalists by that of _Mastacembelus_. They have sometimes in ichthyological systems been referred to the Scombridæ and other marine families, from the circumstance that the dorsal fin anteriorly is composed of spines. But, in addition to the general shape of the body, their affinity to the eel is attested, by their confluent fins, by the absence of ventral fins, by the structure of the mouth and its dentition, by the apparatus of the gills, which opens with an inferior slit, and above all by the formation of the skeleton itself.[1] [Footnote 1: See GÜNTHER'S _Acanthopt. Fishes_, vol. iii. (Family Mastacembelidæ).]