BY J. DOUGLAS OGILBY. 125 



distance behind the base of the pectorals, with a slender spinous 

 and five soft rays : pectorals rather small, moderately pointed, 

 Avith 13-15 rays, those in the upper half of the fin the longest, 

 the upper ray simple and somewhat inspissate : caudal fin emargi- 

 nate, with short deep peduncle. Scales large, cycloid, smooth, 

 not deciduous, the posterior border being more or less truncated, 

 especially on the tail; cheeks, opercles except the outer ridge of 

 the preopercle, and occiput scaly, the rest of the head naked; 

 dorsal and anal fins without a basal scaly sheath; no enlarged 

 scales at the base of the tirst dorsal, pectoral, or ventral fins, and 

 no scaly process between the latter; lateral line wanting; a series 

 of large open pores from the maxillary symj^hysis along the lower 

 border of the preorbital, passing upwards in front of and above 

 the eye to the occiput, where it connects with a similar series 

 extending from the mandibulary symphysis below the eye and 

 round the naked outer preopercular surface. Vertebras 33 to 37 

 (22 + 1 5 in Rliombatractiis Ji'iviatilis). Air-vessel large and 

 simple. Abdominal cavity very large, extending backwards far 

 beyond the vent, the intestines very long and convoluted. 



Etymology : — p6fj.idos, rhomb; arpaKTos, a spindle; in allusion 

 to its shape. 



Type : — Aristeus fitzroyensis, Castelnau. 



D i s tri bu t ion : —Fresh waters of Australia as far south 

 as the 32nd parallel, and of southern New Guinea. 



The sexual differences are strongly marked in these fishes, both 

 as regards the form of the body and the development of the fins. 



In adult males the depth of the body is much greater than in 

 females of the same age; for instance, in a series of specimens of 

 Khumh((.tr((ctu,s fluviatilis, collected from a single haul in Yulpa 

 Creek, near Deniliquin, the depth of the males is from 2 J^ to 2j, 

 of the females from 3i to 3|- in the total length; this variation is 

 entirely due to the slight development in the latter of the post- 

 occipital convexity, which is so pronounced a character in the 

 males, the rostro-dorsal contour in the females being gently and 

 evenly arched from the extremity of the snout to the caudal 

 peduncle. 



