4. NASEUS 351 



cupies the whole of the anterior side of the pracopcrciiliim. The 

 praeorbital is thin and very elongate, and does not enter the orbit, 

 except by a cartilaginous process ; the remainder of the infraorbital 

 ring is very narrow and, posteriori}-, in immediate contact with the 

 epitympanic. The limbs of the pra^operculum meet at a very obtuse 

 angle, and the posterior is twice as long as the inferior. Operculum 

 rather narrow and elevated, not extending downwards to the angle 

 of the praooperculum, where it is replaced by the suboperculum ; the 

 latter is not much smaller than the operculum. Interoperculum very 

 small. 



The bones of the humeral arch are rather strong : suprascapula 

 small, firmly united with the skull ; scapula long, sword-shaped ; 

 coracoid very long and strong, straight, with a longitudinal ridge on 

 its inner side. The cavity for the pectoral muscles is deep, but not 

 so broad as in Acanthurus ; its bottom is thin and transparent, though 

 nearly entirely osseous, the ulna having a small foramen, the radius 

 a larger and a smaller one. Cai-pal bones very small. The piibic 

 bones are ver}- long, slightly bent, and firmly attached to each other ; 

 each is formed by a narrow vertical lamella terminating in a siyii- 

 form process anteriorly. 



There are nine abdominal and thirteen caudal vertebral, the length 

 of the former portion of the vertebral column being to that of the 

 caudal as 1 : 2-3. The vertebras are slightly compressed ; the anterior 

 short, the middle and the caudal ones rather long. The apophyses are 

 of moderate length and strength, and dilated posteriorly into a more 

 or less broad lamella ; the lamella) of tlie neurals and interneurals of 

 the abdominal vertebrae are broad enough to form together one con- 

 tinuous osseous plane, without free spaces between the single bones. 

 The first interneural is strong, bent forwards, so that its upper extre- 

 mity overlaps the occipital region of the skull ; it is provided supe- 

 riorly with a subglobular cavity, in which a round bony tubercle (a 

 rudimentary first dorsal spine) moves ; this interneural does not ter- 

 minate in a spine directed forwards, as in Acanthurus. The second 

 interneural is firmly attached to the first ; the interneurals of the 

 following dorsal spines are dilated superiorly into a slightly concave 

 and oblong plate, and one always corresponds to a single neural, 

 whilst each neural and haemal of the caudal vertebra? always sup- 

 port two or three interneurals and intcrha^mals of the soft rays. 

 The first haemal and interha^mal form one strong bone, much bent 

 forwards, and slightly dilated at its inferior extremity ; the five fol- 

 lowing interhaemals are fixed to it. Ribs moderately developed, with 

 epipleurals. 



lines. 



Length of the first vertebra 0^ 



of the second vertebra 1 



of the third vertebra 1^ 



of the fourth vertebra 2g 



of the tenth vertebra 4 



of the fourteenth vertebra 4^ 



of the eighteenth vertebra 5 



