ACIPENSER! D.E. 281 



(Synonymy of American examples.) 



Acipenser oxyrhynchus, Mitchell, Trans. Lit. and Phil. Soc. New York, i, p. 462 ; 

 Lesueuer, Trans. Amer. Phil. Soc. (new series) i, p. 394 ; De Kay, New York 

 Fauna, Fish. p. 346, pi. lviii, fig. 189 ; Ayres, Boston, Jouvn. Nat. Hist, iv, 

 p. 287 ; Storer, Mem. Am. Acad, ii, p. 499, and viii, p. 431, pi. xxxv, f. 4. 



Huso oxyrhynchus, Dumeril, p. 172 ( ?. old specimen). 



Acipenser (Antaceus) Lecontei, Dumeril, 1. c. p. 177, pi. xvi, f. 1. 



D. 35-40, P. - 2 g^g, V. 23-24, A. 23-25, C. 100-125. 



Shape of the body somewhat pentagonal with five rows of osseous plates or 

 shields, one at each angle ; the body tapers off gradually to the base of the 

 caudal fin, while the head similarly tapers to the end of the elongated snout. 

 Length of head 4 to 5, of caudal fin 4| to 5|, height of body 8 to 10 times 

 in the total length. Eye small* and possessing peculiarities pointing to its 

 affinity to Amphibia and Reptilia (Max Schultze, Meder. Ges. Bonn. 1872). 

 Opercle large, fiat, and rugose, due to depressions, resembling thimble marks, or 

 else granulated or striated. Snout usually pointed and about half the length of the 

 head or even one-third or less, as it varies considerably in different specimens. 

 The osseous shields on the surface of the head are not invariably similar in each 

 specimen. Mouth placed on the under-surface of the head below the eyes ; its 

 jaws protractile, the premaxillaries passing round the front and upper edge of the 

 mouth, while the maxillaries are small, placed laterally and articulated with the 

 premaxillaries and also with the palatines. The lower jaw chiefly formed of two 

 bones united at the symphysis, laterally there is a cartilage. Lips fleshy, lobate, 

 while in the lower jaw there is usually a median depression. Barbels four 

 placed in a transverse line across the ventral surface of the snout, about midway 

 between its extremity and the anterior edge of the mouth. Teeth absent except in 

 very young. Fins dorsal situated near the commencement of the caudal, which 

 latter is heterocercal, and bilobed, the upper being the longer, at its base anteriorly 

 is a bony plate having a posterior blunt upward but short prolongation, which is 

 followed by eleven or twelve short undivided bony rays, the whole constituting a 

 fulcrum. Anal below the posterior half of the dorsal and anteriorly with several 

 undivided rays. Pectoral inserted low down, on a level with the lower edge of 

 the gill-cover, its first ray strong. Ventral, when laid flat, reaches about half- 

 way to the base of the anal. Shields the dorsal plates or shades are those most 

 developed, consisting of from eleven to thirteen, and with the highest point of 

 their keel nearest the front edge in the anterior plates, but near their hind edge in 

 the posterior plates; however, the shape varies much with age. The lateral shields 

 consist of from twenty-six to thirty-three along the middle of the side and are 

 continued to the caudal fin, while there exists an interspace between them. The 

 ventral rows of shields are less developed than the lateral or dorsal rows. The 

 shin may be either smooth, granulated, pointed, or more or less covered with small 

 rough osseous points, which, in some specimens, are frequently star-shaped, and 

 occasionally arranged in oblique rows. Colours brownish, lightest beneath. 



This species has been sub-divided into the sharp-nosed form and the blunt- 

 nosed, Acipenser latirostris, Parnell, who considered it differed from the common 

 form, in having the tip of the nose broader than the mouth ; in the keels of the 

 dorsal plates being but slightly elevated, and its barbels placed nearer the tip of 

 the snout than the mouth. Ball remarked that he did not think the broadness 

 or sharpness of the nose a specific distinction, as no two of his specimens 

 could be said to agree in the form of the nose or the arrangement of the scales on 

 the nose and head. Thompson remarked that he had long felt certain that the 

 precise form (of the bony plates on the heads of sturgeons) is of no value as a 

 specific character ; the form, too, of the anterior extremity of the fish is also 

 liable to much variation from being pointed to rounded. These views have since 

 been generally accepted. 



* For observations on the structure of the Retina in Sturgeons, see II. M tiller, Comptes Kendus, 

 1856, p. 743. also Ann. and Mag. Nat. Hist. 1856. xviii, p. 492. 



