354 



U S. P. R. R EXP. 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 up as the specimens enlarge in size. 



List of specimens. 



Family STURIONIDAE, SwaiES. 



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 (Spalulariae] , else provided with longitudinal series of rather large, bony shields, between 

 which much smaller dermic productions may often be observed (Acipenserini) . 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. 



STN. Sturioniens, Cuv. Regn. Anim. II, 1 7, 140 ; 2d ed. II, 1829; &, ed. illustr. Poiss. 349. 



Sturionidae, SWAINS. Ess. Class. Fish. II, 1839,193. DEKAY, New Y. Faun. IV, 1842, 344. STOKER, Synops. 1846,247- 



Sturionideae, RICHARDS. Faun. Bor. Amer. Ill, 1836, 278. 



Acipenserini, MULL. Verg. Anat. Myxin. I, 1836 ; &, in Weigm. Archiv fur Naturg. 1845, I, 119. 



Spatulariae, MULL. Vergl. Anat. Myxin. I, 1836 ; &, in Weigm, Archiv fiir Naturg. 1845, I, 119. 



Jlcipenseridae , BONAP. Sagg. Distr. metod. Anirn. Vertebr. 1831. AGASS. LaKe Super. 1850, 263. 



Jlcipenserides, AGASS. Rech. Poiss. foss. II, ii, 1833, 277. 



These fishes constitute the order of Cliondrostean ganoids of Professor Muller, by whom they 

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

 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 : Scaphirliynclms, amongst Acipenserini, 

 Polyodon and Planirostra, which constitute the group of Spatulariae. 



ACIPENSER, Artedi. 



GEN. CHAR. Body sub-fusiform, elongated, tapering posteriorly, provided with five longitudinal series of bony shields, the 

 dorsal and lateral series extending from the thoracic arch to the caudal fin, whilst the abdominal series run from the base of the 

 pectorals to that of the ventrals, whence an odd series follows the under aspect of the tail to the caudal fin. Head of moderate 

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

 which are inserted four hanging down, simple or fringed barbels. Lips simple. Branchial apertures separated under the 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. 



SYN. Jldpenser, ARTEDI, Gen. Pise. ed. Walbaumi, 1792, 498. LINN. Syst. Nat. ed. XII&amp;lt;i I, 1766, 403. GMEL. in Linn. 

 Syst. Nat. ed. XIII, I, in, 1788, 1483. Cuv. Regn. Anim. II, 1817, 141 ; 2d ed. II, 1829 ; & ed. illustr. 

 Poiss. 349. RAFIN. Icbtli. Ohiens. 1820, 79. FITZ. & HECK, in Ann. Wien. Mus. Naturg. I, 1835 ; &, in 

 Zool. Abhandl. Ann. Wien. MUS. Naturg. I, 1841, 264. DEKAY, New Y. Faun. IV, 1842, 344. 

 STORER, Rep. Fish. Mass. 1839, 178; &, Synops. 1846, 247. DUM. Ichthyol. analyt. 1856, 156. 



