362 FISHES. 



the Common Sturgeon of the United States (A. maculosus), 

 which sometimes crosses the Atlantic to the coasts of Great 

 Britain ; GiildensttTedt's Sturgeon (A. giUdenstcedtii), common 

 in European and Asiatic rivers, which yields more than one- 

 fourth of the caviare and isinglass exported from Eussia; 

 the Common Sturgeon of Western Europe {A. sturio), which 

 attains to a length of 18 feet, and has established itself also 

 on the coasts of Eastern Korth America. 



ScAPHiRHYNCHUS.- — Suout spatulate ; posterior part of the tail 

 attenuated and depressed, so that it is entirely enveloped by the 

 osseous scutes. Spiracles none. The caudal rays do not extend 

 to the extremity of the tail, which terminates in a filament. 



Four species are known : one {S. flatyrliynclviLs) from the 

 river-system of the Mississippi, and the three others from 

 Central Asia ; all are exclusively freshwater fishes ; their 

 occurrence in so widely distant rivers is one of the most 

 striking instances by which the close affinity of the North 

 American and North Asiatic faunas is proved. 



Second Family — Polyodontid.e. 



Body naked, or with minute stellate ossifications. Mouth 

 latercd, very loide, with minute teeth in both jrcirs. Barbels 

 none. Caudcd fin with fiidcra. Dorsal and anal fins cipproxi- 

 niate to the eaiuhd. Four [/ills and c( halfi ; no o'percidar gill 

 or 2Jseudol)ranchi(i . 



PoLYODON (Spatularia). — The snout is produced into an ex- 

 ceedingly long, shovel-like process, thin and flexible on the sides. 

 Spiracles present. Gill-cover terminating in a very long tapering- 

 flap. One broad branchiostegal. Each branchial arch with a 

 double series of verj^ long, fine, and numerous gill-rakers, the two 

 series being divided by a broad membrane. Air-bladder cellular. 

 Upper caudal fulcra narrow, numerous. 



The single species, P. folium, occurs in the Mississippi, 



