34 PISCES : — GLANIOSTOMI. — VIU. 



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-biadder large, simple; 

 stomach not caecal, 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. 



SCAPHIEBYNCHUS, 30. 



offl. Spiracles present; snout sub-conic; rows of bony shields nowhere con- 

 fluent, the tail not depressed nor mailed ; gill rakers lanceolate. 



ACIPENSEK, 31. 



30. SCAPHIRHYNCHUS Heckel. {ScapUrhynchops Gill.) 

 {<TKa<f>ri, spade ; pvy)(os, 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. (n-Xarvs, flat; piyxos, 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 6 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. (A. 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 



