[Jordan and Evermann, 1896-1900, p. 2683.]
This little flatfish is left-handed (eyes on the left-hand side and viscera at the left-hand edge as the fish lies), with a wide mouth gaping back as far as the forward edge of the eye; with a nearly straight lateral line; and with both of its pectoral fins well developed, though the one on the eyed side is considerably larger than its mate on the blind side. Its left-hand ventral fin stands on the midline of the body, but the right-hand ventral fin is a short distance above it on the blind side, and while the two ventral fins are alike in females, the one on the blind side is much the [page 295] longer of the pair in males. The body is ovate in outline and very thin. The long (ventral and dorsal) fins are of moderate breadth, with the dorsal fin (78 to 83 rays) originating over the forward margin of the eye, the anal (left-hand edge) fin (61 to 67 rays) originating a little in advance of the pectorals; and the caudal fin rounded. The scales are so large that there are only about 40 rows of them along the lateral line.
Fish living at different depths vary so widely in the number of fin rays that future studies may reveal the existence of distinct races, if not of species.
Light brown above, with the scales usually more or less outlined with darker brown; brownish white below.
Maximum length about 7 inches.
This little flatfish parallels the summer, four-spotted, and sand flounders (the latter its closest Gulf of Maine ally) in its left-handedness. But it is distinguishable from all of these by its nearly straight lateral line; by the great disparity in size between its two pectoral fins; and by its very large scales. Its narrow shape and the fact that none of its dorsal fin rays are branched are further points of distinction between it and the sand flounder; also it is much smaller at maturity than any of the flatfishes that are common in the inner parts of the Gulf of Maine.
Little is known of its habits. It is found chiefly in water deeper than 40 fathoms but it has been trawled as shoal as 12 fathoms. Apparently it spawns from spring through summer, for we have found females with well-developed ovaries in February, while Goode had ripe ones in September. It is not large enough to be of commercial value, but we can witness that it is excellent on the table.
Eastern coast of America, along the outer part of the continental shelf from the southwestern part of Georges Bank to the offing of Charleston, S. C., where the Blake took it many years ago, usually at depths of 40 to 200 fathoms, but occasionally as shoal as 12 to 18 fathoms.
A fish occupying this geographic province is misnamed when it is called "Gulf Stream," but this is the only English name by which it has been known.
This little flatfish has never been reported from the inner [page 296] parts of the Gulf, nor is it to be expected there, to judge from its general distribution. But the Albatross I took one in a tow net over the southwestern part of Georges Bank at about the 82 fathom (150 meters) contour line. And subsequent captures of scattered specimens in that general neighborhood in 1931 by the Albatross II; at 8 stations (30 specimens) between the offing of Nantucket and longitude about 67° 10' W., in 41 to 150 fathoms, by the Albatross III in May 1950; and on those same general grounds in 39 to 65 fathoms by the Eugene H in late June 1951, show that its regular range extends eastward far enough to include not only the slope of Nantucket Shoals, but the southwestern sector of Georges Bank arc as well, at the appropriate depth. And it must be considerably more plentiful on the outer part of the shelf off southern New England, for the Albatross III has trawled a considerable number of them there, including one catch of 100 off Montauk Point, in February 1950, and another of as many more off Rhode Island on May 13, 1950, at 41 to 50 fathoms.
 A second species of this genus (C. unicornis Goode 1880) may be expected on the outer slope of Georges Bank in depths of 100 fathoms and more, since it has been taken off Marthas Vineyard in 115 to 150 fathoms. The male is separable from C. arctifrons by the fact that there are several short spines on the eyed side of the head above the upper lip (the head of arctifrons is spineless although old fish may have a bony protuberance on the snout). Further points of distinction are that unicornis has fewer fin rays (only about 74 to 77 dorsal rays and 60 anal rays) and that its body is broader (actually higher). Parr (Bulletin of the Bingham Oceanographic Collection, vol. 4, art. 1, 1931) has published a revision of the genus Citharichthys of the western Atlantic.
We have towed the pelagic larvae of still a third small deep-water flounder (Monolene sessilicauda Goode 1880) off the seaward slope of Georges Bank (Bull. Mus. Comp. Zool., vol. 41, No. 8, 1917, p. 277), while the adults have been trawled in depths of 100 fathoms and more off Marthas Vineyard and thence westward and southward along the continental slope. It is left-handed like the summer, four-spotted, and sand flounders, with arched lateral line, but it has no pectoral fin on the blind side. For a detailed description of it see Goode and Bean, Smithsonian Contrib. Knowl., vol. 30, 1895, p. 452.
 Goode and Bean (Smithsonian Contrib. Knowl., vol. 30, 1895, pp. 443-444) give a long list of localities where it has been trawled, along the continental shelf from the offing of Nantucket to the offing of Charleston, S. C.
 Station 20045, lat. 40° 18' N., long. 68° 09' W., February 22, 1920.