Figure 175.— Lactoria fomaainii: posterior view of 



orbit (cross section of skull; dashed lines 

 represent cut surfaces of frontals. pterosphenoids, 

 prootics, and parasphenoid), 65.2 mm SL, Hawaii. 



summarized here. The most generalized condition of the 

 caudal skeleton is found in Lactophrys trigonus and the 

 two species of Rhine somus, the haemal spine of the 

 penultimate vertebra being relatively large and autog- 

 enous and the haemal canal passing through it and into 

 the caudal plate to exit at a foramen just below the 

 region of the centrum, the foramen marking the region of 

 fusion between what in more generalized plectognaths 

 are the parhypural and lowermost hypural. All three 

 species have three postanal vertebrae. The moderately 

 specialized condition of the caudal skeleton is found in 

 Lactoria cornuta and the four species of Acantho- 

 stracion, the haemal spine of the penultimate vertebra 

 being reduced in size and fused to its centrum, while the 

 haemal canal pierces and exits in the caudal plate just as 

 in Lactophrys and Rhinesomus. There are three post- 

 anal vertebrae in Lactoria cornuta, four in A. polygonius, 

 A. guineensis, and A. notacanthus, and five in A. quad- 

 ricornis. Since all ostracioids with the exception of A. 

 quadricornis have 18 vertebrae, and quadricornis 19, it is 

 assumed that 18 is the generalized number and that the 

 addition of a vertebra in quadricornis has taken place in 

 the postanal series. 



The most specialized condition of the caudal skeleton 

 is found in Lactoria fomasinii, the two species of Ostra- 

 cion, the two species of Tetrosomus, and in Rhyncho- 

 stracion rhinorhynchus. In these species the haemal 

 arches and spines of all the postanal vertebrae are usual- 

 ly much reduced in size, solid, fused to the centra, and 

 not pierced by the haemal canal, which also does not 

 enter the foramenless caudal plate. Of these species, the 

 solid haemal spines are best developed in Ostracion 

 tuberculatus (illustrated here), the haemal spines being 



shorter in 0. lentiginosum (Tyler 1963a:fig. 13, which in- 

 correctly shows nontrifid neural spines) and just as 

 rudimentary if not more so in Tetrosomus and Rhyncho- 

 stracion. There are four postanal vertebrae in Ostracion 

 and Rhynchostracion, and three in Lactoria and 

 Tetrosomus. 



All species of ostraciids have 9 abdominal and 9 caudal 

 (10 caudal in A. quadricornis) vertebrae, and all have 7 

 predorsal vertebrae, with the postanal, flexibly ar- 

 ticulated, vertebrae varying from 5 to 3. 



The postcleithrum is nearly always composed of two 

 pieces, both of which, but especially the ventral piece, 

 are relatively thin and delicate, only the anterior end of 

 the dorsal piece around its region of articulation with the 

 cleithrum being of much strength. Only in the single 

 specimens examined of the two species of Tetrosomus 

 was the division into two pieces not seen, and it may 

 have simply escaped notice in the posterior half of the 

 bone which tends to break away from the front portion 

 during dissection and hold fast to the carapace. 



In all ostraciids the distal end of the first anal fin basal 

 pterygiophore is expanded into a pair of anterolateral 

 wings more or less surrounding the rear half of the anus 

 and supporting the carapace in this region. The carapace 

 has additional specialized supporting structures around 

 both the dorsal and anal fins in the Indo-Pacific species, 

 but not in those of the Atlantic. In addition to the trifid 

 neural spines of two or more of the postdorsal vertebrae 

 that broaden the base of support for the carapace in the 

 Indo-Pacific species, the last dorsal and anal fin basal 

 pterygiophores are also variously modified to help sup- 

 port the carapace. 



Just above its distal end the last anal fin basal pteryg- 

 iophore is always laterally expanded into a shelf upon 

 which the carapace rests. In Lactoria cornuta the shelf is 

 mainly a simple lateral expansion, but in L. fomasinii 

 and all of the other Indo-Pacific species it is expanded 

 anteriorly as well as laterally into a pair of broad antero- 

 laterally directed prongs supporting the carapace. 



The last dorsal fin basal pterygiophore, just below the 

 distal end, is variously expanded laterally and posterior- 

 ly into a supporting flange. In Ostracion, Rhynchostra- 

 cion, and Lactoria cornuta this basal portion of the last 

 dorsal fin basal pterygiophore is much expanded antero- 

 posteriorly and closely held between the stout neural 

 spines of the 11th and 12th vertebrae, while the distal 

 portion of the pterygiophore is expanded both laterally 

 and posteriorly into a shelf upon which the carapace 

 rests. The posterior expansion of the distal end of the 

 pterygiophore usually makes contact with the neural 

 spine of the 13th vertebra. In Lactoria fornasinii the dis- 

 tal end of the last dorsal fin basal pterygiophore is only 

 slightly expanded laterally and posteriorly into a sup- 

 porting shelf and the basal portion is rodlike, not ex- 

 panded anteroposteriorly. Moreover, the trifid neural 

 spines of the 14th to 16th vertebrae are not as massive in 

 L. fornasinii as in L. cornuta, and the neural spine of the 

 13th vertebra in L. fornasinii is long and slender and not 

 in contact with the last pterygiophore rather than mas- 

 sive and in contact with it, while that of the 12th verte- 



