_Teuthis triostegus_, of Japan and Polynesia and the East Indies, is covered with cross-bands alternately black and pale. In Hawaii this is replaced by the very similar _Teuthis sandwichensis_. Many species are found about Hawaii and the other Polynesian Islands. _Teuthis achilles_ has a large blotch of brilliant scarlet on the tail, and _Teuthis olivaceus_ a bright-colored mark on the shoulder. _Teuthis lineatus_, yellow with blue stripes, a showily colored fish of the coral reefs, is often poisonous, its flesh producing ciguatera. _Zebrasoma_ differs from _Teuthis_ in having but 4 or 5 dorsal spines instead of 10 or 11. In this genus the soft dorsal fin is very high. _Zebrasoma flavescens_, sometimes brown, sometimes bright yellow, is common in Polynesia; _Zebrasoma veliferum_, cross-barred with black, is also common. _Ctenochætus_ (_strigosus_), unlike the others, is herbivorous and has its teeth loosely implanted in the gums. This species, black with dull orange streaks, was once tabu to the king of Hawaii, who ate it raw, and common people who appropriated it were put to death. In _Xesurus_ the caudal lancelet is replaced by three or four bony tubercles which have no sharp edge. _Xesurus scalprum_ is common in Japan, and there are three species or more on the west coast of Mexico, _Xesurus punctatus_ and _Xesurus laticlavius_ being most abundant. In _Prionurus_ (_microlepidotus_) of the tropical Pacific the armature is still more degraded, about six small plates being developed. In _Acanthurus_ (_Monoceros_, _Naseus_), the unicorn-fish and its relatives, the ventral fins are reduced, having but three soft rays, the caudal spines are very large, blunt, immovable, one placed in front of the other. In most of the species of _Acanthurus_ a long, bony horn grows forward from the cranium above the eye. This is wanting in the young and has various degrees of development in the different species, in some of which it is wholly wanting. The species of _Acanthurus_ reach a large size, and in some the caudal spines are bright scarlet, in others blue. _Acanthurus unicornis_, the unicorn-fish, is the commonest species and the one with the longest horn. It is abundant in Japan, in Hawaii, and in the East Indies. _Axinurus thynnoides_ of the East Indies has a long, slim body, with slender tail like a mackerel. =Suborder Amphacanthi, the Siganidæ.=—The _Amphacanthi_ (ἄμφϊ, everywhere; ἄκανθα, spine) are spiny-rayed fishes certainly related to the _Teuthididæ_, but differing from all other fishes in having the last ray of the ventrals spinous as well as the first, the formula being I. 4, I. The anal fin has also six or seven spines; and the maxillary is soldered to the premaxillary. The skeleton is essentially like that of the _Acanthuridæ_.