84 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



L. 5-6 feet. Mississippi Yalley and rivers of the Southern States ; gen- 

 erally abundant. 



(Squalus spathula Walhanm, Artedi Pise. 1792, 522: "Pohjodon fcuille" Lac<?pMe, 

 Hist. Nat. Poiss. i, 402 : P. folium Schneicler ed. Bloch, Syst. Iclith. 457 : Spatularia 

 reticulata Shaw, Gen. Zool. 1804, v, 362 : Platirostra edentula (adult) Le Sueur, Journ. 

 Acad. Nat. Sci. Phila. 227 : P. folium Gunther, 346.) 



Oedee H.-GLANIOSTOMI. 



[The Sturgeons.) 



A prsecoracoid arch. No symplectic bone. Maxillary present. 'No 

 suboperculum or preoperculum. Interoperculum present. Mesoptery- 

 gium distinct. Interclavicles present. Basihyals and superior cerato- 

 liyal not ossified. Branchihyals osseous. This grouj) is composed of the 

 single family Acipenseridie. (^Aavtc, a cat-fish, Silurus ; aroim^ mouth.) 



Family XXVI.— ACIPENSERIDiE. 

 {The Sturgeons.) 



Body elongate, subcylindrical, armed with five rows of bony buclclers, 

 each with a median carina which terminates in a spine. A median dor- 

 sal series, and a lateral and abdominal series on each side, the abdomi- 

 nal series sometimes deciduous. Between these the skin is rough, with 

 small irregular plates. Snout produced, depressed, conical or subspat- 

 ulate. Mouth small, inferior, protractile, with thickened lips. No 

 teeth. Four barbels in a transverse series on the lower side of the 

 snout in front of the mouth. Eyes small; nostrils large, double, in front 

 of eye. Gills 4. An accessory opercular gill. Gill membranes united 

 to the isthmus. No brauchiostegals. Maxillary bone distinct from the 

 premaxillary. Head covered with bony plates united by sutures. Fin- 

 rays slender, all articulated. Vertical fins with fulcra. Pectorals 

 I)laced low. Yentrals many-rayed, behind middle of body. Dorsal 

 placed posteriorly. Anal somewhat behind it, similar. Tail heterocer- 

 cal, the lower caudal lobe deyeloped. Air-bladder large, simple, con- 

 nected with the oesophagus. Pseudobranchite small or obsolete. Stom- 

 ach without blind sac. Eectum with a spiral valve. Pancreas divided 

 into pyloric appendages. 



Large fishes of the seas and fresh waters of northern regions. Most 

 of the species are migratory, like the salmon, which are found in the 

 same waters. Genera 2, species about 20, although more than five 

 times that number have been described. The American species esiDCci- 



