FISHES OF THE GENTTS ACENTROPHORUS. 



27 



without further description. One or two remarks only are 

 necessary. The suture between the opercular and subopercular 

 plates varies considerably in position, but nearly always leaves 

 the suboperculimi as the larger bone, except in A. glaphyrus. 

 The branchiostegal rays number nine or ten on each side (text- 

 fig. 7). (Traquair thought there were " few, about seven.") 

 Traquair suspected the presence of a gular ; if there was a gular, 

 however, it must have been a very delicate plate, for in the 

 numerous specimens that ought to show it there is no definite 

 trace of it. The only example which does show anything that 

 could well be taken for a gular is Kirkby's type-specimen of 



Text-figure 6. 



vx- 



-pop 



Acentrophoriis alius. Head showing dentition ; Sunderland Museum. c.Jii/., 

 ceratobyal ; cor., circuinorbitals (thi'ee bordering frontal, three more between 

 parasphenoid and lower jaw); dn., dentary ; /?•., frontal; hJii/., hj^pohj'al; 

 /iw., hj'omandibular : i.op., interoperculum ; w,r., maxilla ; ojt*., operculum ; 

 p.op., preoperculum ; p.ft., palato-pterygoid with teeth ; f.sp., parasphenoid ; 

 s.op., suboperculum ; v.t., vomerine teeth ; x., left premaxilla, or possibly 

 the bodj^ of the vomer. About four times natural size. 



A. alius., the head of which is represented in text-fig. 13. The 

 plate marked x in this figure is a thin, detached bone, of much 

 the size and shape that the gular would have to possess. 



The opercular bones and the roofing bones of the head are 

 ornamented with fine vermicular raised lines. The course of the 

 principal sensory canals of the head can be traced fairly com- 

 pletely. The nasal bones are too thin and badly preserved to 

 show pits or grooves, but the frontal often shows a line of four 

 pits on each side near the orbital margin, and grooves and pits 

 carry the line backwards along the outer side of the squamosal 

 to cross the outer end of the supratemporal and the antero- 



