FISHES. PLATE 4.
Chelmon marginalis.
Drawn on Stone by W. Mitchell. Hullmandel & Walton Lithographers.
This fish is described in the Annals of Natural History from a dried specimen brought from Port Essington by Mr. Gilbert. It has very much the form of Chelmon rostratus, but wants the eye-like spot on the dorsal. Several examples in spirits were brought by the officers of the Beagle from the north-west coast of Australia, all of which show a broad band passing between the dorsal and anal fins, which was not visible in the dried specimen. This band is bounded anteriorly by one, and posteriorly by two whitish lines. In the Annals the anal fin is described as being more angular than the dorsal, but in the specimens in spirits the reverse appears to be the case. This variation depends on the degree or expansion of the fins, and both may be much rounded by pulling the rays apart. The exact distribution of the bands may be clearly made out from the figure, which is very correct. The rays of the fins probably vary in number in different individuals, and our careful enumeration of those specimens kept in spirits, as recorded above, gives two or three soft rays more in the dorsal and anal, than we were able to detect in the dried skin. Length, 5 1/4 inches.
HABITAT. Northern and north-western coasts of Australia.
ASSICULUS.
CH. GEN. Corpus compressissimum, assulaeforme: caput crassius, minus altum, declive. Os parvum. Maxilla inferior porifera, ore clauso ascendens, hinc, ore hiante, ultra maxillam speriorem modice protractam extensa.
Preoperculum margine integro nec spinifero, disco arcto, inaequali, esquamoso, genam squamosam postice et infra cingens. Operculum tridentatum: Suboperculum crenatum; utrumque et interoperculum latiusculum squamis satis magnis tecta. Dentes villiformes, minuti cum dente canino in media utroque latere maxillae inferioris et trans apicem utriusque maxillae dentibus quatuor (vel sex) fortioribus, altioribus, in serie exteriori ordinatis. Dentes vomeris et palati acuti, stipati minuti. Dentes pharyngei, acerosi inequales, acuti.
Membrana branchialis radiis sex sustentata, interoperculis liberis, accumbentibus tecta.