284 Sir J. Richardson on Australian Fish. 



Threpterius, Eichardson. 



(QpeTrri'ipios, ad alendum idoneus.) 



Genus piscium acanthopterygiorum Cheilodactylis aflSue. Corpus 

 catheto-plateum, ovato-oblongum, squamosum. Caput aliquantulum 

 parvum, cute porosa tectum, absque spinis, angulis vel aciebus ser- 

 ratis osseis. Os ut in Cheilodactylis exteusibile. Dentes in pre- 

 maxillaribus, mandibuia trigonioque vomeris unii serie instruct!, bre- 

 vissimi, parvi, subconici. Ossa palatis laevia. Gense craniumque 

 esquamosse. Os preorbitale angustum. Operculum subtriangulare 

 squamis tectum. Membrana branchiostega radiis sex curvis, satis 

 validis sustentata. Squamae laeves nee dentatae ; linea lateralis recta. 

 Radii pinnarum pectoralium inferiores simplices. Pinna dorsi e 

 nucha fere usque ad caudoe pinnam regnans, squamulis apud radios 

 instructa, membrana inter spinas profunde emarginata ; lobulo tamen 

 membranaceo e summis spinis pendente. Pinnae ventrales thoracicae 

 sed a gula paulo remotae. 



The characters are deduced from dried specimens, and the pharyn- 

 geal teeth and structure of the intestinal canal are unknown. The 

 jaw teeth are not strictly disposed in a single row, since a few minute 

 ones form a row behind the others in front of the premaxillaries ; 

 but these can scarcely be ^^sible in the recent fish. The cherron of 

 the vomer is acute and projects a little. The orifice of the mouth is 

 rather larger than in the Cheilodaetyli, but the jaws are extensible in 

 about the same degree. The maxillary bone wants the flat thin plate 

 near its head which exists in the Cheilodaetyli and glides beneath 

 the preorbitar. The latter bone is narrow, its width not being equal 

 to one-third of the diameter of the orbit. The eye is comparatively 

 large, three diameters and a half of the orbit being equal to the entire 

 length of the head, and two of these diameters measure the distance 

 between the hinder edge of the orbit and the tip of the gill-cover. 

 The position of the eye is high enough to encroach upon the profile. 

 The cheek equals the diameter of the orbit in breadth ; the disk of 

 the preoperculum is also wide, and the interoperculum moderately so. 

 The operculum and suboperculum conjointly have a triangular form ; 

 the former is notched, and the latter is prolonged by a membranous 

 tip, which forms the apex of the gill-cover. Both these bones are 

 densely scaly ; there is also a row of scales on the interoperculum, 

 partially overlaid by the thin edge of the preoperculum, and the tem- 

 ples are also scaly. The rest of the head is without scales, but the 

 mucous skin, full of canals and pores, which envelopes the head, pre- 

 vents us from ascertaining the exact extent of the scales, at least in 

 the dried specimens. The top of the head is destitute of scales to the 

 occiput, but in the Cheilodaetyli, dense, small scales extend forward 

 on the skull to before the eyes. In the absence of thick fleshy lips, 

 the genus differs from Cheilodactylus. Tlie preorbitar is neither wide 

 enough nor long enough to conceal the maxillary, which however 

 enters partially beneath its edge. The thin crescentic border of the 

 preoperculum is striated, but not crenated. The same kind of streaks 

 or furrows may be discerned, though not so readily, in some Cheilo- 



