526 CENTRISCIDJB. 



the other, on the side of the heaa and at a small distance from the 

 orbit. The operpulum is ovate, nearly twice as long as high ; the 

 suboperculum broad anteriorly, curved and tapering posteriorly ; the 

 prse- and inter- operculum are united into one bone, the inferior por- 

 tion of which is extremely thin, transparent and flexible, forming a 

 broad membranaceous margin at the throat, which is continued by 

 that of the belly. 



Branchiostegals three, extremely feeble ; four gills, pseudobranchise 

 well developed ; gill-opening of moderate width. 



The back of the fish is cuirassed by a bony sheath, which extends 

 downwards nearly to the middle of the side, has a shallow notch 

 before and above the pectoral fin, and tapers behind into a point 

 projecting beyond the end of the tail. It is composed of five median 

 paij-s of narrow bones, six lateral ones of a lamelliform shape, and, 

 finally, of a single long dagger- shaped bone which terminates the 

 cub'ass. The sutures of all these bones are deeply serrated, except 

 the longitudinal suture along the vertebral Hne, which is simple. The 

 long moveable spine in which the cuirass terminates is evidently an 

 interneural, since, in the second species, the first spine of the dorsal 

 fin is joined to it ; it is situated in quite a horizontal direction, in 

 the same line as the upper profile of the body. 



The humerus also contributes to the bony covering of the body : 

 a long horizontal portion of it extends from the opcxculimi to the 

 base of the pectoral fin ; it fits into the shallow notch of the dorsal 

 cuirass mentioned, and is of a lanceolate shape, tapering into a point 

 posteriorly. 



The inferior half of the side of the trunk is covered by a trans- 

 parent tough covering, which passes into a broad cutting fringe 

 inferiorly ; this fringe extends the whole length of the abdomen, 

 and the whole covering is supported by the coracoid and by seven 

 or eight ribs. 



The vertical fins are crowded together on the short and elevated 

 tail : this part is covered with soft skin, moveable, propelling the 

 body through the water by its lateral motion ; its length, from the 

 point where it is free to the base of the caudal fin, is less than the 

 depth of the body. As the cuirass has a horizontal direction, the 

 taU is, as it were, obliquely pressed downwards. Three slender 

 dorsal spines are situated below, and nearly parallel to, the inter- 

 neural ; they are connected with the interneural and with one another 

 by a tough membrane. The second or soft dorsal fin is immediately 

 behind the first, and composed of ten or twelve simple rays, the 

 posterior of which are quite rudimentary and point obliquely down- 

 wards. The caudal fin is obtusely rounded, directed downwards, and 

 has also simple rays ; the anal fin has not an unusual position, and 

 terminates, like the dorsal, closely before the caudal. The pectoral 

 is obliquely truncated, inserted upon the middle of the depth of the 

 body, at a considerable distance from the head, as stated above. The 

 ventral fins are rudimentary, apparently composed of three rays ; 

 they are inserted upon the cutting edge of the membranaceous fringe 

 of the abdomen, below the third rib, at a chstance from the root of 



