3. TETEAGONUKUS. 407 



of the head one-fifth ; the diameter of the eye equals the extent of 

 the snout (in mature specimens), and is nearly one-fourth of the 

 length of the head. The iirst dorsal spine pungent, the others fili- 

 form ; tlie last dorsal rays produced, reaching to the base of the 

 caudal. The ventrals end in a tliread-like tip which overlaps the 

 commencement of the anal. The first dorsal and the anal conmienee 

 in nearh' the same vertical. An even black stripe replaces the usual 

 silveij- band, and is continued forwards over the gill-cover, upper 

 lialf of the eye, and sides of the snout ; it occupies the fifth series of 

 scales and the adjoining parts of the fourth and sixth. 

 Freshwater streams of Port Essington, 



a. Three inches long : skin. King's lliver, near Victoria. — Type of 



the species. 



b. Adult : skin. Port Essington. From Mr. Gould's Collection. 

 c-e. Twenty-one lines long : skins. Severn River (New South 



Wales). — I am not quite sm-e whether these specimens really 

 belong to A. nigrans. The form is nearly the same, but they 

 have a very indistinct blackish band on the tail. 

 /. Adult: skin. Australia. 



Second Group. TETRAGONURINA. 



Teeth not very small, compressed ; scales keeled and striated. Tlie 

 first dorsal continued on to the second. Air-bladder none. Pyloric 

 appendages numerous. 



3. TETSAGONURUS. 



Tetragonurus, Risso, Ichth. Nice, p. 347. 



Body subcj'lindrical, somewhat elongate ; snout of moderate length, 

 obtuse ; lower jaw elevated, with a convex dental margin. Teeth in 

 single series, ■ compressed, triangular, rather small ; teeth on the 

 palate. Scales rather small, with deep strife, those of every single 

 transverse series coherent. Ventrals abdominal, but inserted below 

 the middle of the pectoral. Air-bladder none. Pyloric appendages 

 numerous. 



Mediterranean, and the neighbouring parts of the Atlantic. 



This genus has been annexed to very different families : first to the 

 MugUklce by Cuvier, then to the Scombridce by Lowe, and finally to 

 the Notacantli'ini by Miiller. The attempt of the latter is certainly 

 the most unfortunate, and I doubt whether Miiller has known the 

 fish, except from Valenciennes' description. Even when the artificial 

 group called by Midler Notacanthini is divided into natural families, 

 Tetragonurus has no aflinity whatever either to Notacantlms or to 

 Masfacembelus. "WTien Mr. Lowe places this fish among the Scom- 

 beroids of Cu\'ier, he implies, in the words by which he modifies his 

 view, tliat he means that portion of them which I have called Tri- 

 chiuricke. But in Tetragonurus the ventral fins are truly abdominal, 



