290 MR. C. TATE REGAN ON [ISToV. 4, 



the barbs of tlie dorsal spine, if distinct, are usually in four series. 

 There are 19 or 20 vertebrae. In this genus the gradation is 

 perfect from those species without barbs to those with four equi- 

 distant series of strong barbs. 



6. Alutera Cuv. — Differs from Pseudomonacanthus in that the 

 dorsal spine is feeble, the ventral spine is absent, the pelvis is 

 entirely concealed, and the dorsal and anal rays usually in greater 

 number. The lower jaw is projecting, the gill-openings oblique 

 and below the eye, and the vertebras number 21. 



7. Psilocephalus Swainson. — Diffei-s from Alutera in its more 

 elongate body, very feeble dorsal spine, lower jaw with a barbel, 

 gill-openings in advance of the eye, and vertebrae numbering 

 29-30. 



This family has well-defined characters, and the relations of 

 the various genera are very clear ; its division into subfamilies is 

 without value, and if Balistes and Psilocephalus are to rank as 

 distinct families, Monacanthus, Alioier^a, Paraluteres, and Pseud- 

 aluteres should receive the same treatment, and the Balistidse (as 

 here understood) be raised to the rank of a division. 



Some authors have stated that the symplectic is not ossified in 

 the fishes of this and the next family. I find that in all cases it 

 is present as a small but distinct ossification attached to the lower 

 margin of the metapterygoid between stylo-hyal and quadrate ; 

 the stylo-hyal has shifted its attachment forwards from the hyo- 

 mandibular to the anterior part of the lower margin of the 

 metapterygoid, and has, as it were, pushed the symplectic in 

 front of it. 



Family 4. Ostraciontid^. 



Closely allied to the Balistidse, but with feeble parapophyses, 

 no epipleurals, prseorbital not ossified, palatine immovable, pelvis 

 absent, no spinous dorsal, no ventrals, soft dorsal and anal short. 

 Clavicles, coracoids, and post-clavicles much expanded. Scales 

 represented by large, juxtaposed, bony plates, mostly hexagonal 

 and immovably united. 



Genera. 



1. ARACANAGray. — Body ovate or orbicular. Carapace ceasing 

 before the dorsal and anal fins, with more or less distinct longi- 

 tiidinal ridges, 3 on each side, and often a dorsal and ventral 

 ridge; some isolated plates on the caudal peduncle. D. 10-12. 

 A. 10-12. Caudal truncate or rounded. Sixteen vertebrae, not 

 elongate, subequal in length except the two preceding the square 

 hypural, which are shortened. 



2. OsTRACiON Linn. — Body 4- or 5-sided ; carapace extending 

 beyond and closed behind the anal fin, with two prominent ridges 

 on each side and often a dorsal ridge. Caudal peduncle naked. 

 D. 9-10. A. 9-10. Caudal trimcate or rounded. Sixteen 



