332 U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



HYODON, Lesu. 



GEN. CHAR. Body very much compressed, deep upon its middle, covered with large scales, deeper than long, disposed upon 

 transeverse oblique series ; ventral line sharp, but not serrated. Head small ; snout rounded ; jaws equal. Teeth on the jaws 

 vomer, palatines, and tongue. Eyes very large. Gill apertures continuous under the throat. Dorsal fin opposite the anal 

 Caudal fin furcated, else crescent-shaped posteriorly. Lateral line nearly straight, running along the middle of the flanks. 



SYN. Hyodon, LESU. in Journ. Acad. Nat. Sc. Philad. I, i, 1818, 364. RAFIN. Ichth. Ohiens. 1820, 41. Cuv. Regn. Anim. 

 2d ed. II, 1829 ; &, ed. illustr. Poiss. 283. DEKAY, New Y. Faun. IV, 1842, 265. STOKER, Synops. 184C, 

 210. Cuv. & VAL. Hist. nat. Poiss. XIX, 1846, 307. 

 Glossodon, HECK, in Russeg. Reisen, I, 11, 1842, 1033. 



Uafinesque lias a genus Glossodon, which Heckel appears to have ignored ; adopting Lesueur s 

 genus Hyodon, he sub-divides it into three subgenera : Amphiodon, Glossodon, and Clodalus. 

 It is not our present purpose to inquire into this subject beyond introducing here, into its natural 

 family, a fish that was supposed at one time to belong to that of Cyprinoids, with the 

 peculiar and exceptional characters of having teeth upon the tongue. 



HYODON TEKGISUS, Lesu. 



Moon-eye. 



PLATE LXXV, FIGS. 1 4. (By error on the plate : figs. 4 7.) 



SPEC. CHAR. Head contained five times and a half in the total length ; snout rounded, sub-conical. Posterior extremity of 

 maxillar bone extending to a vertical line drawn posteriorly to the pupil. Eye very large, sub-circular ; its diameter entering 

 about four times in the length of the side of the head. Anterior margin of dorsal fin somewhat nearer the tip of the caudal than 

 the occiput. Base of anal fin entering about four times in the total length. Insertion of ventrals nearer the extremity of the 

 snout than the terminus of the anal. 



SXN. Hycdon lergum, LESU. in Journ. Acad. Nat. Sc. Philad. I, i, 1818, 366. RICHARDS. Faun. Bor. Amer. Ill, 1836, 235. 

 KIRTL. Rep. Zool. Ohio, 1838, 170, and 195 ; &, in Bost. Journ. Nat. Hist. V, in, 1846, 338. DEKAY, New Y. 

 Faun. IV, 1842, 265; pi. XLI, fig. 130. STORER, Synops. 1846, 210. Cuv. & VAL. Hist. nat. Poiss. XIX, 

 1846, 309. 



The &quot;moon-eye,&quot; or &quot;lake&quot; and &quot;river herring,&quot; as this fish is sometimes called, has been 

 made the subject of much comment by the various writers who have spoken of it. Several 

 species have been put on record without criticism ; adopted by some, rejected by others, so that 

 up to the present day we are still left in doubt as to the number of species of the genus Hyodon 

 inhabiting the fresh waters of North America. Let us hope that the time is not far when the 

 Museum of the Smithsonian Institute shall be in possession of preserved specimens from every 

 locality where these fishes are found, so as to enable us to institute a thorough examina 

 tion of their zoological as well as anatomical characters, in order to settle a question so much 

 controverted. 



One fact is already clear to our mind, that the differences in the outline of the anal fin 

 alluded to by Lesueur and Valenciennes are traits indicative of the sexes, and should H. clodalus 

 prove specifically distinct from H. tergisus the distinction will be based upon very different 

 characters. The above diagnosis, which we offer, of H. tergisus, is drawn up with a view of 

 assisting future observers should they be prevented from forwarding specimens to Washington 

 for ulterior comparisons. 



