34 PISCES: — GLANIOSTOMI. — VIII. 



brancliiostcgals ; liead covored by bony plates joined l)y sutures; 

 gill membranes joined to istiimus ; vertical fins witli fulcra; dorsal 

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

 stomach not ca-cal, with j)yloric appendages; rectum wiih spiral 

 valve. Seas and rivers of northern regions ; feeding on small 

 animals and plants sucked in through the tube-like mouth, (ienera 

 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 coalesciMit behind the dorsal, so that the depressed tail is 

 completely mailed; gill rakers small, fan-shaped, ending in 3 or 4 points. 



ScAniiitiivNtiiis, 30. 

 aa. Spiracles present; snout sub-conic; rows of bony shielils nowliere con- 

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



ACIl'ENSER, 31. 



30. SCAPHIRHYNCHUS Ileckel. (Scaphirhynchops Gill.) 



{(TKii'prj, spade ; pvy^os, snout.) 



40. S. platyrhynchus (Rafinesque). Suovel-nosed Stur- 

 geon. White 8tik(;kun. Body elongate, tapering into the 

 slender depressed tail, which extends in the young beyond C. as a 

 slender fdament; shields sharjily keeled; dorsal shields 15 to 18; 

 lateral, 41 to 4G; ventral, 11 to 13. L. 5 feet. Miss. Valley, etc., 

 commoa. (TrXarur, flat; pvy)^os, snout.) 



31. ACIPENSER (Artedi) Linnnpus. (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 iU 



41. A. Bturio L. Common Sturgeon. First dorsal fulcrum 

 somewhat enlarged, its surface rough; dorsal shields 9 to 11; 

 lateral shields 2G 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. oxyrhjnchHs Mitchill, the American form; said to 

 have usually fewer lateral shields.) (/>"•) (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 \i\-\ ; dnrsiil shields 15 or 16. 



42. A. rubicunduB Lc Sueur. Lake Sturgeon. Rock Stur- 

 geon. First dorsal fulcrum slightly enlap.;ed ; dorsal shi«.'Ids 15; 

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



