280 Mr. C. T. Regan on the 



or less regularly convex anteriorly, fitting the concavity 

 formed by the facets of the l)a3i- and exoccipitals, the second 

 without ribs, as usual in Perciform fishes, the next seven 

 bearing ribs, and succeeded by thirteen caudals. The ribs 

 are veiy similar in each case, but in Luvarus they are more 

 blade-like. A notable difference is tliat in the Acanthuridae 

 the prcecaudals have well-developed parapophyses, to which 

 epipleurals are attached, and subsessile ribs ; Luvaras, on the 

 contrary, has only rudimentary parapophyses, apparently no 

 epipleural><, and sessile ribs. 



According to Siebenrock * in Luvarus the post-temporal 

 is attached above to the skull, and lower down emits a short 

 rounded process which joins the squamosal, whilst its distal 

 end is long and attached to the clavicle, there being no 

 supra-clavicle, unless this bone represents the co-ossified post- 

 temporal and supra-clavicle. As this bone is attached distally 

 to the clavicle and proximally to the same parts of the skull 

 as the post-temporal in Acanthurid^, tlie probability that it 

 represents both supra-clavicle and post-temporal is very 

 great; in having this latter bone forked Luvarus is less 

 specialized than the Acanthuridse, in which family the post- 

 temporal is simple, owing to the reduction of the process which 

 joins it to the squamosal. It is worth noting that in many 

 characters Luvarus approaches more closely to Naseus than to 

 any other genus, notably in the long anal fin extending to 

 the vent, which is situated just behind the origin of the 

 ventrals, and in the physiognomy of the head. Naseus is the 

 only genus of Acanthuridai with pointed teeth in the jaws, 

 and in some species these are quite feeble, so that in this 

 character also it approaches Luvarus, the young of whicii 

 have a single series of small pointed teeth in the jaws. The 

 similarity of the keel-like plates on the caudal peduncle in 

 both genera is evide it, and the posterior nostril is noticeably 

 small in Naseus and minute in Luvarus. 



Apparently the remarkable feature of the loss of the ante- 

 rior rays of the dorsal and anal fins during growth is peculiar 

 to Luvarus^ and not paralleled in the Acanthuridae. 



The Luvaridge may be defined thus : — 



Similar to the Acanthurid*, but with feebly ossified 

 skeleton, very weak dentition, and post-temporal forked. 

 Prajcaudal vertebrse with rudimentary transverse processes ; 

 ribs sessile, blade-like, inserted at the middle of the length 

 of the centrum ; epipleurals absent. Anterior rays of dorsal 



* Anil. Ilofmus. Wieii, xvi. 1901, pp. 119 & 125. 



