324 



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



SYN. Osmerus, ART. Gen. Pise. ed. Walbaumi ; 1792, 56 ; &, Synon. 1703, 21. Cuv. Regn. Anim. II, 1817, 162; 2d 

 ed. II, 1829 ; &, ed. illustr. Poiss, 257. STOREU, Rep. Fish. Mass. 1839, 108 ; &, Synops. 1846, 197. 

 DEKAY, New Y. Faun. IV, 1842, 243. Cuv. & VAL. Hist. nat. Poiss. XXI, 1848, 36c. 



The following species has so much the general aspect of Argentina that on a former occasion 

 we have described it under the latter heading. The argentine tint which pervades over the 

 middle of the flanks, a comparatively smaller mouth than in the known species of Osmerus, the 

 presence of six branchiostegal rays, and the position of the ventral fins, were as many traits 

 which seemingly militated in favor of the genus Argentina. After considering, however, the 

 value attached to the dentition in the family of Salmonidae, we have deemed it expedient to 

 ascribe said species to the genus Osmerus, in which it was subsequently placed by Dr. W. 0. 

 Ayres, of San Francisco. By its small teeth it reminds us of 0. microdon, from Scandinavia. 



OSMERUS PRETIOSUS, G r d. 

 PLATE LXXV, FIG. 5. (Under the name of Argentina prctiosa.*) 



SPEC. CHAR. Posterior extremity of maxillar bone extending to a vertical line drawn in advance of the pupil. Eye large 

 and circular ; its diameter contained about four times in the length of the side of the head. Origin of dorsal fin somewhat 

 nearer the extremity of the snout than the tip of the caudal fin. The adipose is situated opposite the posterior fourth of the 

 anal. The origin of the ventrals is placed somewhat behind a vertical line drawn from the anterior margin of t he dorsal fin- 

 Scales of moderate development. Upper surface of head and back yellowish ; outline of scales dotted with black. Sides of 

 head and middle of flanks of a shining, silvery tint ; lower half of flanks and belly dull yellowish. 

 SYN. Argentina preliosa, GRD. in Proc. Acad. Nat. Sc. Philad. VI f, Aug. 1854, 155. 

 Osmerus elongatut, AYRES, in Proc. Cal. Acad. Nat. Sc. I, Deo. 1854, 17. 



The body is gracefully elongated, compressed, fusiform in its outline, the largest specimens 

 observed measuring over seven inches in total length, in which the head enters somewhat over 

 five times. The eye is large and circular, its horizontal diameter being contained a little over 

 four times in the length of the side of the head. The posterior extremity of the maxillar 

 bone extends to a vertical line which would pass in advance of the pupil. The origin of the 

 dorsal fin is a little nearer the tip of the lower jaw than the base of the caudal fin. The adipose 

 fin is situated opposite the posterior fourth of the anal. The caudal fin is shorter than the 

 head. The origin of the ventrals is placed somewhat behind a vertical line drawn at the anterior 

 margin of the dorsal, their extremities not extending as far as the vent. The pectorals are a 

 little more slender and longer than the ventrals. 



Br. VI : VI ; D 11 ; A 13 ; C 10, 1, 9, 8, 1, 8 ; V 1, 8 ; P 1-16. 



The scales are of medium size. The upper region of the head and back are yellowish, the 

 outlines of the scales being minutely black dotted. The sides of the head and the middle 

 of the flanks are silvery, shining ; the lower part of the flanks and the belly being dull 

 yellowish. 



Reference to the figure. Plate LXXY, fig. 5, represents Osmerus pretiosus, size of life. 



List of specimens. 



