246 PROCEEDINGS OF THE ACADEMY OF [1889. 



heterocercal, the lower caudal lobe developed, the upper lobe covered 

 with rhomboid scales. The vertical fins with fulcra, and all the fin- 

 rays slender and articulated. 



Air-bladder large, simple, attached to the dorsal wall of the 

 abdominal cavity, and in free communication with the esophagus. 

 Stomach without blind sac. Rectum with a spiral valve. Pancreas 

 divided into pyloric appendages. 



Large fishes found in the seas and fresh-waters of northern regions. 

 Most of the species are migratory, inhabiting the same waters as the 

 salmon. About 20 species are known, of which 6 are found in 

 American waters. The species fall into two very natural genera. 



Analysis of Genera of Acipenseridae. 



a. Spiracles obsolete ; snout broad, shovel-shaped, much de- 

 pressed above ; rows of bony shields confluent behind the dorsal, so 

 that the depressed tail is completely mailed ; gill-rakers small, fan- 

 shaped, ending in 3 or 4 points. Scaphirhynchus, 1. 



act. Spiracles present ; snout sub-conic ; rows of bon} r shields no- 

 where confluent ; the tail not depressed or mailed ; gill-rakers 

 lanceolate. Acipenser, 2. 



SCAPHIRHYNCHUS. 



Aeipenser Rafinesque, Ichth. Ohiensis, 80, 1820 (platorhynchus). 



Seaphirhynchus Heckel, Ann. AViener Mus. Naturgesch. I. 71, 

 1835 {rafinesquii). (Not Scaphorhynchus of Prince Maximilian, 

 1838, a genus of birds. ) 



Scaphirhynchops (Gill MSS.) Jordan and Copeland, Bull. Buff. 

 Soc. Nat. Hist. 161, 1876 {platyrhynchus). (Substitute for Seaphi- 

 rhynchus regarded as preoccupied). 



Type : Seaphirhynchus rafinesquii Heckel= Aeipenser platorhynchus 

 Rafinesque. 



Etymology, skdphe, a skiff; rhynchos, snout. 



Analysis of Species of Seaphirhynchus. 



a. Plates between ventrals and anal large, in two rows of three 

 in each row, and one median row of one plate. Space between 

 dorsal and lateral shields of small bony plates in 4 or 5 series. Last 

 dorsal shield of moderate size, less than half length of one before it. 

 Dorsal shields 18 (15-20); lateral shields 46 (41-46); ventral 

 shields 13 (11-13). D. 32; A. 20. Shields sharply keeled and 

 spines well developed. Body elongate, tapering into the slender 

 depressed tail, which extends in the young beyond the caudal as a 



