326 U. 8. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



quite extend as far as the vent. The pectorals are smaller than the ventrals, posteriorly 

 rounded, and far from reaching the origin of the ventrals. 



Br. VIII: VIII; D 1, 10 + 1 ; A 1, 19 + 1 ; C 8, 1, 9, 8, 1, 7 ; V 1, 8 ; P 1, 11. 



The scales are of moderate development, longer than deep, anteriorly sub-truncated, pos 

 teriorly rounded, exhibiting conspicuous concentric stria, but no radiating furrows. The 

 lateral line is very conspicuous, linear, and nearer the back than the belly. 



The upper surface and sides of the head are greyish, whilst the dorsal region is greyish olive. 

 Upon the upper portion of the flanks, along the course of the lateral line, exists a yellowish 

 orange streak, dotted or rather speckled with black, the abdominal region being yellowish, 

 unicolor, with a metallic reflect. The dorsal and caudal fins assume the tint of the back ; the 

 anal, ventrals, and pectorals that of the belly. 



References to ike figures. Plate LXXV, fig. 1, represents Thaleichthys stevensi, size of life. 

 Fig. 2 is a dorsal scale. Fig. 3, a scale from the lateral line. Fig. 4, a scale from the abdo 

 minal region. 



List of specimens. 



COREGONUS, Artedi. 



GEN. CHAR. Body more or less elongated, sub-fusiform in profile. Head sub-conical ; mouth rather small ; snout truncated, 

 sometimes quite protruding beyond the lower jaw ; both jaws always toothless. Teeth on the tongue. Branchial apertures 

 continuous under the throat. Ventrals inserted posteriorly to the anterior margin of the dorsal fin, and situated opposite the 

 adipose fin. Caudal fin furcated. Scales of moderate development. 



SYN. Coregonus, ART. Gen. Pise. ed. Walbaumi, 1792,53 ; &, Synon. Pise. 1793, 18. Cuv. Regn. Anim. II, 1817, 162; 2d 

 ed. II, 1829; &, ed. illustr. Poiss. 259. RICHARI.S. Faun. Bor. Amer. Ill, 1836, 309. DEKAY, New Y. 

 Faun. IV, 1842, 247. STORER, Synops. 1846, 199. Cuv. & VAL. Hist. nat. Poiss. XXI, 1848, 454. 

 AGASS. Lake Super, 1850, 336. 



In order that the value of the characters assigned to the genus Coregonus in the above 

 diagnosis should be fully appreciated by our readers, it must be stated that we adopt the genus 

 Argyrosomus of modern writers, characterized by a pointed snout and a prominent lower jaw, 

 which projects beyond the upper one. The mouth in Argyrosomus being also more deeply cleft 

 and the teeth on the tongue more conspicuously developed than in Coregonus, properly so called. 

 Moreover, the premaxillar bones in Argyrosomus exhibit a row of small teeth, a character which 

 leads to the genus Thymallus, a species of which inhabiting some of the fresh waters of the 

 British possessions in North America. 



COREGONUS WILLIAMSONI, Grd. 

 PLATE LXVI. 



Si EC. CHAR. Head contained five times and a half in the total length. Mouth small ; posterior extremity of maxillar bone 

 not extending quite as far as the anterior rim of the orbit. Eye moderate, sub-circular ; its diameter entering about five times 

 in the length of the side of the head. Anterior margin of dorsal fin nearer the posterior edge of the base of the adipose than 



