There is no adipose dorsal in the Haplomi, the dorsal is inserted far back, and the •head is generally scaly. Most, but not all, of the species are of small size, living in fresh or brackish waters, and they are found in almost all warm regions, though scantily represented in California, Japan and Polynesia. The families are Esocide or pikes, Umbridce or mud-min nows, Poeciliida or killifishes, and Amblyopsid• or blind-fishes of the caves. The Gonorhynchicke and the extinct families of Crossognatahid• and Cobitopsidce may be doubtfully added to this group.
Order most of the remaining bony fishes constitute a natural group for which the name Acanthopterygii (aKavga, spine; nrEpou fin or wing), may be used. This name is often written Acanthopteri, characters may be lost through degeneration. Thus fin-spines, otenoid scales and the homo cercal tail are lost in the cod-fishes, the con nection of ventrals with shoulder-girdle fails in certain peculiar forms, and the development of the air-duct is subject to all sorts of variations. In one family even the adipose fin reappears.
The Acanthopterygii or preferably Acanthop teri, the Physoclysti of Muller, the Thoracices of older authors, and the Ctenoidei of Agassiz, include substantially the same series of forms.
Among the many subordinate groups, sub orders or super-families, a few stand out as susceptible of definition. Among these is the group of Salmopercce, composed of perch-like fishes, with spines in the fins and with ctenoid scales, yet retaining at the same time the ab dominal ventrals and the adipose fin of the salmon. This constitutes the family of Per copsicke, trout-perches or sand-rollers. The ex tinct Erismatopterida• and Asineopida' probably belong here.
The sub-order synentognathi agree exter nally with the Haplomi, but have the lower a form equally correct and more euphonious and convenient. These are characterized, with numerous exceptions, by the presence of spines in the fins, by the connection of the ventral fins to the shoulder-girdle, by the presence, in gen eral, of more than one spine in the anterior part of dorsal and anal fins, and as a rule of one spine and five rays in the ventral fins, and by the absence in the adult of a duct to the air bladder. Minor characters are these: The pectoral fins are inserted high on the shoulder pharyngeals solidly united, and the lost in the course of development. The families
are Belonicke, the gars, Scombresocicke, the sauries, or half-beaks, and Exoccetidce or flying-fishes. This order and the Haplomi are joined by Hay under the name of Mesichthyes, the groups forming a perfect transition from soft-rayed to spiny-rayed fishes.
The group of Percesoces has the general traits of the spiny-rayed fish, with the ventral fins abnormal. Here belong the Sphyrenide or barracudas, the Atherinsde or silversides, and the Mugilido or mullets. Another sub-order, Rhegnopteri, includes the Polynemidce or thread has proposed to unite them as a distinct order. Phthinobranchii (peivuv, waning). The Hemi branchii include the families Gasterosteide (sticklebacks), Protosyngnathide (extinct), fins. Other transitional forms, with the ven trals abdominal, and spines usually present in the fins, constitute the sub-orders of Hemi branchil, Lophobranchii and Hypostomides. In all of these the bones of the gill-arches are duced in number, and the gill-structures are tinctly degenerate. For this reason Dr. Hay Auforhynchicke, Fistulariicke (cornet fishes), Aulostomida' Urosphenidce (extinct), Rhamphosidce (extinct), Marco rhamphosidce and Centriscidce (shrimp-fishes). The more degenerate sub order of Lophobranchii includes the Solenos tomide, the Syngnathidce (pipe-fishes), and the Hip pocampidce or sea-horses. The singular order of Hypostomides includes the Pegaside (sea-moths or sea-dragons).
In another sub-order we may place the Berycoidei, fishes perch-like in general structure and usually well armed, with the ventral fins thoracic, but their number of rays never I, 5, the typical number in all perch-like forms. The berycoids are especially characterized by the presence of the orbitosphenoid bone, a struc ture wanting in all perch-like families; are the earlies in time of the fishes of this pattern, appearing in the Cretaceous or earlier. The families are Berycidce, Trachichthxidce, Nolo centride or Polyttuxiide, and Monocentride or pine-cone fish.
Another group or sub-order Zeoidei, agrees well with the beryces in the presence of more than five soft rays in the ventral fins and in the armature of the fins. It differs, however, in the character of the skeleton, the post-temporal, especially being adnate to the skull, as in the butterfly-fishes or Chdtodontida.