70 Miscellaneous. 



operculum. The intcropcrculum is more or less concealed within 

 the pracoporculura ; at least in its anterior part, or that which is 

 joined to the jaw, and sometimes throughout its whole extent, it 

 presents the form of a rod. The second case is that of the Balistes ; 

 the former that of the AcantJiuri, in which it acquires the form of a 

 very narrow plate only in its posterior part. 



The hyoid bone is attached to tlic temporal wing at hut little dis- 

 tance from the postoiur angle of the lower jaw; it is conse(]uently 

 very small. The lateral branches, which bear the branchiostegal 

 rays, have fewer pieces than in other fishes. The unpaired piece, or 

 tail of the hyoid, is very lai'ge, and formed of two long branches 

 uniting at a right angle. 



The bones of tlie slioulder appear, in the part anterior to the 

 pectoral fins, in tlie form of large plates, produced by at least the 

 partial amalgamation of the three bony pieces which, according to 

 Cuvier's nomenclature, form the humerus, radius, and cubitus. The 

 coracoid is greatly developed. The pelvis is much elongated, and 

 the two pieces which form it are more or less soldered together. 



The vertebral column is formed by a small number of vertebrae 

 (about 20 to 22). The dorsal vertebras bear very long vertical 

 neurapophyses and hori/ontiil ha)mapophyscs starting from tho 

 middle of tho vertebra and bearing very small ribs. The caudal 

 vertebra) have the neurapophyses and haimapophyses vortical and 

 much elongated. 



The differences between the skeletons of the Acanthuri and Balistes 

 are but few and of slight importance. 



The Acanthuri have nasal and suborbital bones, which are want- 

 ing in the Balistes ; but these bones are very variable in fishes, and 

 can only furnish secondary characters. 



The dorsal fin is single in the Acanthuri, whilst in the Balistes 

 the spinous and soft rays are separated to form two fins. 



In the Balistes the pra;operculum has its oblique shorter than its 

 horizontal branch ; the reverse is the case in the Acanthuri : con- 

 sequently the branchial fissures and the opercular flaps are larger in 

 tho Acanthuri than in the Balistes. 



In the Acanthuri the dorsal hicmapophyses bear, besides the ribs, 

 some little styles which ascend in the interior of tho muscles, as in 

 the Clupeida). 



"We see therefore that, with the exception of a few differences, the 

 osteological type of the Acanthuri is the same as that of the Balistes. 

 I regret that I am unable to complete this investigation by the 

 comparison of the other organs, which must undoubtedly present 

 resemblances similar to those of the skeletons. I must add, how- 

 ever, that Valenciennes has already indicated the at least apparent 

 similarity presented by the scaling of a species oi Acatithurus (A. 

 scopas) to that of certain lialistiiUc of the genus Monacantlms — a 

 resemblance which had even struck the Dutch of the East Indies, 

 since they confound the ]5alistida) and the Acanthuri under the same 

 denomination, that of Lcervisch, or " leather-fishes." — Comptes 

 Jiendiis, June 17, 1872, pp. 1527-1530. 



