248 PROCEEDINGS OF THE ACADEMY OF [1889. 



Helops Brandt and Ratzeburg, Medizin. Zool. II. 352, 1883 

 (stellatus). 



Antaaeus Brandt, Bull. Acad. Sc. St. Petersboursr, V. 138-141 et 

 179-185, LSI).-) (xolnjpa). 



Lioniscus Fitzinger and Heckel, Ann. Wien. Mus. 370, tab. XXV. 

 f. 3, et XX VI II. f. 5 et 6, 1836 (glaber). 



Type: Acipenser sturio Linnaeus. 



Etymology. Lat. acipenser, a. sturgeon; from akis, point ; pente, 

 five. 



The species of this genus have been multiplied to more than one 



hundred, those in American waters have in particular been unduly 



increased by Auguste Dumeril, who has described about forty from 



specimens in the museum at Paris. All of these nominal species are 



a burden to systematic science. The changes with age in these fishes 



is considerable, the snout becomes shorter and less acute, the spines 



become blunter, the roughness of the plates is generally diminished, 



and the ventral plates often disappear altogether. The number of 



plates is also subject to considerable variation. 



Analysis oj Specie* of Acipenser. 



a. Plates between ventrals and anal large, in one row, or two 

 rows anteriorly and one median row posteriorly of 1 to 4 plates. 



b. Space between dorsal and lateral shields with stellate plates of 

 rather large or medium size, in 5 to 10 series; last dorsal shield of 

 moderate size, more than half length of one before it. 



c. Shields, stellate plates and bony plates on head roughly 

 striated and ridged, and shield-spines strongly developed, presenting 

 a general rough and angular appearance; stellate plates rather 

 large, in about 5 series, densely interspersed with smaller ones. 

 Dorsal shields 11 (9-11); lateral shields 26 (26-30); ventral 

 shields 8 (7-10). D. 33; A. 22. Snout sharp in the young, becom- 

 ing blunt with age, usually rather shorter than the rest of head. 

 Anal nearly as long as dorsal and placed almost entirely posterior 

 to it. Color olive-green, with an olive stripe on the median line of 

 the belly and one each side above the ventral plates, these stripes 

 ceasing opposite the vent. medirostris, 2. 



cc. Shields feebly striated ; stellate plates rather small, in about 

 10 rows, with numerous smaller ones interspersed. Dorsal shields 

 10 (10-14); lateral shields 29 (27-36); ventral shields 9 (8-11). 

 D. 38 ; A. 27. Snout rather sharp, nearly as long as the rest of the 

 head, becoming comparatively shorter and blunter with age. Anal 



