[Jordan and Evermann, 1896-1900, p. 721 Hyporhamphus roberti (Cuvier and Valenciennes) 1846.]
The most striking feature of this halfbeak and one which is enough of itself to mark it off from every other fish known from the Gulf of Maine, is the fact that while the lower jaw is very long, the upper jaw is short.
This is a slender fish, its body only one-sixth to one-tenth as deep as long (younger fish are still more slender), tapering slightly toward head and tail. Its dorsal (14 to 16 rays) and anal (15 to 17 rays) fins are situated far back and opposite each other, as in the silver gar, and are about equal in length and alike in outline. There are no detached finlets between them and the caudal fin. The ventrals stand about midway between a point below the eye and the base of the caudal. The teeth are small and the scales are largest on the upper surface of the head. The beak is much shorter in young fish than it is in adults.
Translucent bottle green above with silvery tinge, each side with a narrow but well-defined silvery band running from the pectoral fin to the caudal fin, the sides darkest above and paler below this band. The tip of the lower jaw is crimson in life, with a short filament, and three narrow dark streaks run along the middle of the back. The forward parts of the dorsal and anal fins and the tips of the caudal fins are dusky. The lining of the belly is black.
Adults are seldom more than 1 foot long.
Tropical and subtropical on both coasts of America and in the Gulf of Mexico; abundant off the South Atlantic United States, not uncommon northward to Cape Cod, and straying to the coast of Maine.
In our cool boreal waters the halfbeak is only a rare stray from the south, previously recorded only twice in the Gulf of Maine, i. e., from Machias and from Casco Bay, Maine, many years ago in each case. We can now add one taken in Quincy Bay, Boston Harbor, July 10, 1951, by Gordon Faust; another off Revere (also in Boston Harbor) on the 19th of the month, by John M. Hodson; a third, taken in a trap at Sandwich, September 24 of the same year, and several dozen taken in a pound net at Small Point, Maine, July 14-15, reported by Leslie Scattergood.
 Should a halfbeak be taken in the Gulf of Maine it would be well to consult Meek and Hildebrand (Field Museum of Natural History, Zool. Series, vol. 15, Pt. 1, p. 232, 1923) for there are several other species that might reach us as strays, either via the Gulf Stream route or from offshore. One, indeed (Euleptorhamphus velox), has been taken at Nantucket. Its lower jaw is even longer and more slender than that of the halfbeak, its body is more flattened sidewise, and its pectoral fins are longer.
 These specimens are in the Harvard Museum of Comparative Zoology.