84 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 
L. 5-6 feet. Mississippi Valley and rivers of tlie Soutliern States ; gen- 
erally abundant. 
(Squalus spatliulaWalhanm, Artedi Pise. 1792, 522: “Polyodon fcuille” Lac^pftde, 
Hist. Nat. Poiss. i, 402 : P. folium Scliueider ed. Bloch, Syst. Ichth. 457 : Spatularia 
reticulata Shaw, Gen. Zool. 1804, v, 362: Platirostra edentula {adnlii) Le Sueur, Jouru. 
Acad. Nat. Sci. Phila. 227 : P. folium Giiuther, 346.) 
Order H.-GLANIOSTOMI. 
[The Sturgeons.) 
A praecoracoid arch. jSTo symplectic bone. Maxillary present. No 
suboperculum or preoperculum. Interoperculum present. Mesojitery- 
gium distinct. Interclavicles present. Basihyals and superior cerato- 
hyal not ossified. Brancliihyals osseous. This group is composed of the 
single family Acipenseridee. a cat-fish, Silurus ; GToya^ mouth.) 
Family XXVI. — ACIPEXSERIDJE. 
[The Sturgeons.) 
Body elongate, subcyliiidrical, armed with five rows of bony bucklers, 
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 defciduous. 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, doable, in front 
of eye. Gills 4. An accessory oi)ercular 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 
placed low. Ventrals many-rayed, behind middle of body. Dorsal 
placed posteriorly. Anal somewhat behind it, similar. Tail heterocer- 
cal, the lower caudal lobe develoi)ed. Air-bladder large, simple, con- 
nected with the oesophagus. Pseudobranchire small or obsolete. Stom- 
ach without blind sac. Pec turn with a spiral valve. Pancreas divided 
into pyloric ai)pendages. 
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 esx)eci- 
