Caudal fin rays. —Ten in number, the uppermost 

 ray and the lowermost ray unbranched, the others 

 becoming increasingly branched toward the middle rays, 

 which are branched in triple dichotomies. The five upper 

 rays articulate by fibrous tissue at their bifid bases with 

 the upper lobe of the fused hypural plate and the lower 

 five rays with the lower lobe. 



DORSAL AND ANAL FINS. 



Fin rays and pterygiophores. — Ten fin rays are 

 present in most specimens; the first ray unbranched, the 

 other rays branched in single or double dichotomies. Dis- 

 tal pterygiophores are either absent or unossified. The 

 bifid bases of the fin rays are supported through fibrous 

 tissue by nine basal pterygiophores. With the exception 

 of the first pterygiophore, all of them are slender rods, 

 cartilage filled at both ends and of decreasing length pos- 

 teriorly in the series. At their dorsal ends these rodlike 

 pterygiophores are somewhat compressed and are closely 

 held to one another by fibrous tissue and slight inter- 

 digitation, with the degree of interdigitation between 

 them increasing with increased specimen size. From the 

 second to the ninth pterygiophore, slight concavities are 

 present in the surfaces of contact of the pterygiophores 

 with each other, so that gaps are present in the other- 

 wise interdigitated surfaces. The first pterygiophore is 

 unlike the others only in that it is expanded anteriorly 

 throughout most of its length into a thin flange. The 

 anterodorsal edge of the first pterygiophore inter- 

 digitates with the posterior edge of the supraneural. The 

 supraneural is a short, laterally expanded, plate whose 

 dorsal surface is convex and whose ventral surface is con- 

 cave. The dorsal surface of the supraneural is in close fi- 

 brous tissue contact with the cuirass. The dorsal fin basal 

 pterygiophores articulate by fibrous tissue between the 

 neural spines of the seventh abdominal to third caudal 

 vertebrae. The articulation of the ninth pterygiophore is 

 somewhat different from the others in that it makes a 

 much more intimate contact with the adjacent neural 

 spine than do the others, for it lies in close apposition 

 with the concave anterior edge of the neural spine of the 

 third caudal vertebra. 



Fin rays and pterygiophores. — Ten fin rays are 

 present in most specimens; the first ray unbranched, the 

 others branched in single or double dichotomies. Distal 

 pterygiophores are either absent or unossified. The bifid 

 bases of the fin rays are supported through fibrous tissue 

 by 9 (occasionally 10) basal pterygiophores. These 

 pterygiophores are basically similar to those of the dor- 

 sal fin in that they are slender rods, compressed at their 

 ventral ends into flattened narrow plates held to one 

 another by fibrous tissue and slight interdigitation. Con- 

 cavities are present in their surfaces of contact with each 

 other so that gaps are present in their otherwise inter- 



digitated surfaces. Whereas all of the dorsal fin pteryg- 

 iophores lie in the midvertical plane of the body, only the 

 last four anal fin pterygiophores lie entirely in this 

 medial plane, the five pterygiophores anterior to them 

 diverging to the right and to the left from their ventral 

 ends, which are in the midvertical plane. The sixth to 

 ninth pterygiophores have their dorsal ends held by fi- 

 brous tissue to the anteroventral surfaces of, respec- 

 tively, the first to fourth caudal vertebrae. The middle 

 region of the posterior edge of the ninth pterygiophore is 

 also held by fibrous tissue to the concavity on the an- 

 terior edge of the haemal spine of the fifth caudal verte- 

 bra. The second to fifth pterygiophores have their flat- 

 tened ventral regions in the midvertical plane, but their 

 long rodlike anterodorsally directed portions lie to the 

 right or to the left of the midline in the anterior portion of 

 the large muscle mass connected to the anal fin (only the 

 two pterygiophores that diverge to the left are shown in 

 the figure of the lateral view of the entire skeleton). The 

 anterodorsal rodlike portion of the first anal fin basal 

 pterygiophore is placed only very slightly to one side of 

 the midvertical plane, either to the right or to the left 

 depending on the individual. The ventral edge of its rod- 

 like portion is expanded into a low and thin keel through- 

 out most of its length. The first pterygiophore has by far 

 the largest distal end of any of the pterygiophores. Its 

 base is expanded anterolaterally to either side to form a 

 U-shaped projection which lies just under the cuirass. In 

 large specimens the usually rodlike dorsal portions of the 

 second to fifth pterygiophores may become laterally ex- 

 panded into thin flanges in the region where these 

 pterygiophores converge toward the midvertical plane of 

 the body. 



Anatomical diversity. — The carapace extends well 

 behind the level of the posterior ends of the dorsal and 

 anal fins and completely encloses the fin bases in all 

 species of the family except Lactophrys trigonus, the lat- 

 ter having the carapace somewhat extended beyond the 

 dorsal and anal fin bases but only completely closed 

 behind the anal fin. Posterior to the dorsal fin in L. 

 trigonus the two posterodorsal extensions of the carapace 

 often closely approach one another in the midline, es- 

 pecially in large specimens, and are separated from one 

 another and from the anterior half of the large fi-ee plate 

 that lies just behind the dorsal fin only by a very narrow 

 scaleless space. In one especially large specimen of L. 

 trigonus examined (ANSP 102757, 366 mm) externally, 

 the posterodorsal extensions of the carapace and the 

 usually free plate are in intimate contact and are as fully 

 interdigitated with one another as are the other scale 

 plates of the carapace, the carapace in this specimen 

 forming a complete wide bridge over the caudal peduncle 

 behind the dorsal fin. 



In most genera (Acanthostracion, Rhinesomus, Lac- 

 tophrys, Tetrosomus) the carapace has a basically tri- 

 angular shape, the horizontal distance between the 

 ventrolateral ridges being greater than between the 

 dorsolateral ridges, with the carapace extended above 

 into a dorsal ridge. A mediolateral ridge is scarcely devel- 



