354 



U S. p. R. R. KXP. AND SURVEYS — ZOOLOGY GENERAL REPORT. 



area may be observed between and behind the ventral fins. These areas exist in the immature 

 state only, and are filled irji as the specimens enlarge in size. 



Family STURIONIDAE, Swairs. 



The skeleton remains in a cartilaginous condition throughout life^ and the vertebral column, 

 instead of vertebrae, consists of a soft chord. The external surface of the body is either perfectly 

 smooth (Spatulariac) , else provided with longitudinal series of rather large, bony shields, between 

 which much smaller dermic productions may often be observed (Acipenser-ini) . The pseudo- 

 branchiae, the accessory opercular gill, and the spiracles exist in various combinations in the 

 several genera which constitute this family. There is but one dorsal fin, situated far back, and 

 nearly opposite to the anal. 



Svw.— S/urioniens, Cuv. Reffn. Anim. II, 1817, 140 ; 2d ed. II, 1829; &, ed. illustr. Poiss. 349. 



S/urtoiii<iae, Swains. Ess. Class. Fish. 11, 1839,193.— DeKay, New Y. Faun. IV, 1842, 344.— Storer, Synops. 1846,2<7- 



Slurionideae, Richards. Faun. Hor. Amer. Ill, 183(), 278. 



..Ocipemerini, Mull. Verg. Anat. Myxin. I, 1836 ; &, in Weigm. Archiv fiir Naturg. 1845, I, 119. 



Sputulariae, Mull. Vergl. Anat. My.xin. I, 1836; &, in Weigm. Archiv fur Naturg . 1845, 1, 119. 



Jlcijitnseridae, Bonap. Siigg. Distr. metod. Anim. Vertebr. 1831. — Agass. LaKe Super. 1850, 2G3. 



Jlciptnserides, Agass. Rech. Poiss. foss. II, ii, 1833, 277. 



These fishes constitute the order of Chondrostean ganoids of Professor Miiller, by whom they 

 are further divided into two families : the Acipenserini, or true sturgeons, with longitudinaj 

 series of bony shields, and the Spatulariae, spoon-bill, or paddle-fish, as sometimes denominated, 

 and in which the skin is naked, or else perfectly free from either shields or scales. 



The generic types of the chondrostean ganoids are all represented in North America, three Of 

 them being altogether peculiar to the latter continent : ScaphirJnjnchus, amongst Acipenserini, 

 Polyodon and I'lanirostia, which constitute the group of Sjmtulariae. 



ACIPENSER, Artedi. 



Gen. Ciiar. — Body sub-fusiform, elongated, tapering posteriorly, provided witli five longitudinal series of bony shields, the 

 dorsal and lateral scries extending from the thoracic arch to the caudal fin, whilst the abdominal scries run from the liase of tlie 

 pectorals to tliat of the vontrals, whence an odd series follows the under aspect of tlic tail to the caiulal fin. lliiul of moderate 

 size, its upper surface cuirassed ; snout elongated, more or less acute. Mouth situated under the snout, tootliless, in advance of 

 which arc inserted four hanging down, simple or fringed barbels. Lips simple. Rrancliial apertures separated under llie throat 

 by an isthmus ; gill covers well developed ; pseudo-branchiae and spiracula both extant. Dorsal fin posterior ; caudal with two 

 unequal lobes; anal situated opposite and somewhat behind the dorsal ; ventrals inserted posteriorly to the middle of the length 

 of the body. 



Swu.—.Qcipcnser, Artedi, Gen. Pise. ed. lyallmimi, 1792, 498.— Linn. Syst. Nat. ed. Xlla I, 1766, 403.— Gmel. in Linn. 

 Syst. Nat. ed. XIII, 1, in, 1788, 1483.— Cuv. Rtgn. Anim. II, 1817, 141 ; 2d ed. II, 1829; &od. illustr. 

 Poiss. 349.— Rakin. Icbth. Ohiens. 1820, 79.— Fitz. & Heck, in Ann. Wicn. Mus. Naturg. I, 1835 ; &, in 

 Zool. Abbandl. Ann. Wien. ^us. Naturg. I, 1841, 264.— DeKay, Now Y. Faun. IV, 1842, 344.— 

 Storer, Rep. Fish. Mass. 1839, 178; &, Synops. 1846, 247.— Dum. Icbthyol. analyt. 1856, 156. 



