176 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Genus 102. ACANTHOCYBIUM Gill. The Petos. 
Body elongate, fusiform; head very long, slender, and pointed, the mandible being longer than 
upper jaw; jaws forming a sort of beak; cleft of mouth extending to below eye; posterior part of 
maxillary covered by the preorbital; both jaws armed with a close series of trenchant teeth, ovate or 
truncate, their edges finely serrate; villiform teeth on vomer and palatines; gills as in Xiphias, their 
laminae forming a network; scales small, scarcely forming a corselet, those along the base of dorsal 
enlarged and lanceolate; keel strong; caudal spinous; dorsal very long, its spines about 25 in number. 
One species, a very large makerel-like fish, widely distributed; especially abundant about the Florida 
Straits. This remarkable genus marks a long step from Scomberomorus toward the type of swordfishes. 
Acanthocybium Gill, Proc. Ac. Nat. Sci. Phila. 1862, 125 (sara= solandri). 
129. Acanthocybium solandri (Cuvier & Valenciennes). “ Ono.” 
Head 4; depth 6.5; eye 5 in snout; gape more than half length of head; premaxillaries in front 
prolonged in a sort of beak, which is nearly half length of snout; teeth somewhat irregular, the 
posterior much the largest, all strong, serrated, about 50 in each jaw. Dorsal spines mostly subequal; 
lateral line descending abruptly under sixteenth dorsal spine, the highest, behind middle of fin, 5.66 
in head; dorsal and anal lobes low; caudal lobes short, very abruptly spreading, their length about 
two-thirds head; pectoral 2.25 in head; corselet small. 
Color steel-blue; dark above, paler below; no distinct markings; young faintly barred; fins colored 
like. the body. 
This fish is not abundant, but a single specimen, 48 inches long, was seen by Doctor Jenkins in 
1889, in Honolulu, and Mr. Snyder obtained it there in 1902. 
The Ono was said by the ancient Hawaiians to be the parent of the Opelu (mackerel). 
Cybium solandri Cuvier & Valenciennes, Hist. Nat. Poiss., VIII, 192, 1831, open sea of the Pacific, exact locality unknown. 
Cybium sara Lay & Bennett, Beechey’s Voyage, Zool., 63, pi. 20, fig. 2, 1849, Loo Choo. 
Cybium petus Poey, Memorias, II, 234, pi. 16, fig. 1, 1860, Habana. 
? Acanthocybium petus Poey, Synopsis, 363, 1868 (Cuba). 
Cybium verany Doderlein, Giorn. de Sc. Nat., Ed. Econ., VIII, 1872, Palermo. 
Acanthocybium solandri, Jordan, Proc. U. S. Nat. Mus. 1884, 119; Jordan & Evermann, Fish. North & Mid. Amer., 876, 1896; 
Jordan & Evermann, Amer. Food and Game Fishes, 288, 1902; Jenkins, Bull. U. S. Fish Comm., XXII, 1902 (Sept. 
23, 1903), 441 (Honolulu); Snyder, op. eit. (.Tan. 19, 1904), 523 (Honolulu). 
Family LIV. LEPIDOPIM.— The Escolars. 
Mackerel-like fishes with the body rather elongate, more or less compressed, covered with minute 
scales; lateral line various, sometimes obsolete, sometimes with a dorsal branch; head large, com- 
pressed, with very strong teeth, usually compressed, some of the anterior canine-like; lower jaw pro- 
jecting; gill-openings wide, the membranes not united, free from isthmus; gills 4, a slit behind fourth; 
opercles in adult unarmed; in young, the preopercle with radiating spines as usual in scombroid fishes; 
dorsal fin long, a notch separating the weak spines from the soft part, which always forms a distinct 
lobe anteriorly, similar in form to the anal fin; finlets often present; caudal peduncle slender, usually 
not keeled, the fin moderate in size, always forked; ventrals small, often reduced to a single spine; 
vertebra; numerous, 82 to 53 in number; pyloric cceca rather few; air-bladder usually present. Colora- 
tion metallic, usually brilliant. Genera about 6; species about 12. Fishes of the high seas, widely 
distributed and descending to considerable depths; usually breeding about rocky islands; most of 
them used as food. The Lepidopidx are closely allied to the Scombridss, from which they diverge in 
the direction of the Trichiuridx. The successive steps are indicated by the progressive elongation of 
the body, the progressive reduction of the ventrals and vertical fins, and on the other hand by -the 
progressive elongation of the lower jaw and the specialization of the dentition. Dr. Lutken calls 
attention to the fact that the Lepidopidx possess a system of dermal or subcutaneous ribs, composed of 
slender bony filaments, close-set, directed backward and upward, and backward and downward from 
the median line. This character has been verified in Thyrsites, Nealotus, and Gempylus. 
a. Body moderately elongate, the dorsal spines fewer than 30, the finlets usually few. 
b. Ventrals well developed, their rays I, 5 Ruvettus, p. 177 
bb. Ventral fins each reduced to a single spine Promelhichthys, p. 178 
aa. Body greatly elongate, the dorsal fin with about 30 spines, the spinous part continuous with the soft part; dorsal and 
anal finlets 6; dentition strong; ventrals I, 5, very small Lemnisoma, p. 179 
