34 PISCES : — GLANIOSTOMI. — VIII. 
branchiostegals ; head covered by bony plates joined by sutures; 
gill membranes joined to isthmus; vertical fins with fulera; dorsal 
and anal posterior; tail heterocercal; air-bladder large, simple; 
stomach not cecal, with pyloric appendages; rectum with spiral 
valve. Seas and rivers of northern regions; feeding on small 
animals and plants sucked in through the tube-like mouth. Genera 
2, species about 20. 
The sturgeons change considerably with age. The snout be- 
comes shorter and blunter, the shields smoother, and some of the 
shields often fall off or are absorbed in old age. 
a. Spiracles obsolete; snout broad, shovel-shaped, depressed above; rows of 
bony shields coalescent behind the dorsal, so that the depressed tail is 
completely mailed; gill rakers small, fan-shaped, ending in 3 or 4 points. 
SCAPHIRHYNCHUS, 30. 
aa. Spiracles present; snout sub-conic; rows of bony shields nowhere con- 
fluent, the tail not depressed nor mailed; gill rakers lanceolate. 
ACIPENSER, 31. 
30. SCAPHIRHYNCHUS Heckel. (Scaphirhynchops Gill.) 
(oxaghn, spade; puyxos, snout.) 
40. S. platyrhynchus (Rafinesque). SHOVEL-NOSED STUR- 
GEON. WHITE StTurGEON. Body elongate, tapering into the 
slender depressed tail, which extends in the young beyond C. as a 
slender filament; shields sharply keeled; dorsal shields 15 to 18; 
lateral, 41 to 46; ventral, 11 to 13. L.5 feet. Miss. Valley, etc., 
common. (zAatus, flat; poyxos, snout.) 
31. ACIPENSER (Artedi) Linneus. (Lat., sturgeon.) 
a. Plates between vent and A. large, in one or two rows. 
b. Space between dorsal and lateral shields with stellate plates of moder- 
ate size in 5 to 10 series: last dorsal shield of moderate size, more 
than half length of one before it. 
41. A. sturio L. Common SturGeon. First dorsal fulerum 
somewhat enlarged, its surface rough; dorsal shields 9 to 11; 
lateral shields 26 to 31; ventral, 9 or 10; 2 rows of 2 shields each, 
with one median shield between vent and anal. D. 40, A. 26. 
L. 8 to12 feet. N. Atlantic, ascending rivers; commonest N., S. 
to S. C. (A. oxyrhynchus Mitchill, the American form; said to 
have usually fewer lateral shields.) (/u.) (Lat., sturgeon.) 
bb. Space between dorsal and lateral shields with minute plates in very 
many series. 
c. Last dorsal shield of moderate size, more than half length of next 
the last ; dorsal shields 15 or 16, 
42. A.rubicundus Le Sueur. LAKE SturRGEON. Rock Stur- 
GEON. First dorsal fulerum slightly enlarged; dorsal shields 15; 
lateral 38, ventral 10; 3 shields in a single row between anal fin 
