34 PISCES : GLANIOSTOMI. VIII. 



branchiostegals ; head covered by bony plates joined by sutures ; 

 gill membranes joined to isthmus ; vertical fins with fulcra; dorsal 

 and anal posterior; tail heterocercal ; air-bladder large, simple; 

 stomach not caical, 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. 



ACIPEXSER, 31. 



30. SCAPHIRHYNCHUS Heckel. (Scapliirliyncliops Gill.) 

 (o-Ka<pr], spade ; pvyxos, snout.) 



40. S. platyrhynchus (Rafinesque). SHOVEL-NOSED STUR- 

 GEON. WHITE STURGEON. 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. (TrXarvs, flat; pvy%os, snout.) 



31. ACIPENSER (Artedi) Linnaeus. (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 fulcrum 

 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 to 12 feet. ~N. Atlantic, ascending rivers; commonest N., S. 

 to S. C. (.4. oxyrhynchus Mitchill, the American form; said to 

 have usually fewer lateral shields.) (Eu.) (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 STURGEON. ROCK STUR- 

 GEON. First dorsal fulcrum slightly enlarged ; dorsal shields 15; 

 lateral 38, ventral 10; 3 shields in a single row between anal fin 



