PH. GREENWOOD 



Fig. 2 The urohyal of four latrid species. A. Acantholatris monodactylus (BMNH unregistered; ex Gough Island); left lateral and ventral 

 views. B. Latris lineata (BMNH 1855.9.19:194); left lateral view. C. Mendosoma lineatum (BMNH 1960.1.8:14-21); left lateral and ventral 

 views. D. Latridopsis ciliaris (BMNH 1872.7.1:31); left lateral and ventral views. Scale in millimetres. Drawn by Gordon Howes. 



the chironemid type is relatively foreshortened (cf Figs 1A & 

 IB). 



A pronounced ventral shelf and overall foreshortening of 

 the bone is also characteristic of the aplodactylid urohyal 

 (Fig. 1C), but in this type the bone is relatively deeper than is 

 the chironemid urohyal, and the dorsal surface is produced 

 into only a narrow shelf. 



When compared with all other types, the cheilodactylid 

 urohyal (Fig. ID) is very distinctive. In lateral view it has 

 virtually the shape of an arrow-head with its tip directed 

 anteriorly, and with the two arms meeting at the somewhat 

 thickened apex from which a dorsally directed process arises. 

 The anterior edges of both arms are slightly broadened to 

 form a very narrow bilateral shelf that does not quite extend 

 to the posterior tip of either arm. Although, morphogeneti- 

 cally, the cheilodactylid type of urohyal could be derived 



from a latrid type by a marked anterior extension and 

 deepening of the latter's posterior indentation, coupled with 

 an increase in the angle subtended by the two arms so 

 formed, the two morphotypes are readily distinguishable. 

 Interestingly, the urohyal in the so-called 'paperfish' juvenile 

 stage (see p. 7) of a 44 mm standard length Cheilodactylus 

 pixi Smith, 1980, resembles that of the latrid type more 

 closely than does this bone in larger specimens; nevertheless, 

 the upper and lower arms of the urohyal in the 'paperfish' 

 stage are more widely separated, the division between them 

 extends further anteriorly, and the anterior body of the bone 

 is less compressed and more barrel-like than that in any of the 

 adult latrid urohyals I have examined. 



In his monograph on urohyal bones Kusaka (1974) 

 described and illustrates this bone in Goniistius zonatus 

 (Cuv., 1839), a taxon now, and previously (Gill, 1862), 



