156 The Ottawa Naturalist. [October 



close to the root of the paddle-snout. They were placed as in s )me of 

 the whales just above the angle of the mouth. The mouth was of 

 enormous capacity, toothless and quite underneath the head, far 

 back as in all sturg-eons. The gape was enormous so that the 

 lower jaw formed a huge tongue-shaped flap, pointed in front and 

 capable of being very widely opened. Next to the absurd elon- 

 gated snout and the great capacity of the mouth, the most notice- 

 able feature was the remarkable leathery operculum. In the 

 Sturgeon it is small and insufficient to cover the red gills, but in 

 Polyodon it sends back a pointed flap long enough to reach nearly 

 half the length of the body. From this upper flap the hind margin 

 of the operculum gracefully curved down and forward and the flap 

 on each side met below and formed a prominent projecting collar 

 in the jugal or throat region. The skin was, soft slimy and naked, 

 in contrast to the enamelled scales and bony plates which cover 

 the skin in other Ganoid fishes. It resembled the smooth integu- 

 ment of the porpoise : but was of a dark bluish purple colour, 

 varied by pale blue wavy lines passing diagonally and slightly 

 opalescent. The opercular flap is traversed by radiating sinuous 

 mucus canals. The paired fins, pectoral and ventral, occupy the 

 characteristic Ganoid position quite underneath the body. They 

 are powerful, and possess a stout and prominent basal part or 

 peduncle. The great dorsal fin and the equally large anal fin re- 

 semble the same members in the Sturgeon : but the basal portion 

 is far more massive and the margin more deeply lunate. The tail 

 is an enormous organ, very deeply forked and the upper lobe is 

 extremely high, and the back bone extends to the tip, a pertect 

 heterocercal caudal fin. All the fins are dusky and leathery like 

 those of a shark. 



An anatomical examination would have revealed many in- 

 teresting features : but it was not possible. It would, for exam- 

 ple, have shown the absence of ribs, the persistence of the gristly 

 rod or notochord, whose sheath never becomes segmented. There 

 is, in Polyodon, no true backbone. The operculum develops a 

 bony basal part : but it is attached to the suspensorium of the 

 jaws, which is cartilaginous, except at the upper part articulating 

 with the periotic surface of the skull. It is interesting to find that 

 the spiracles which, with one exception, are found on the top of 



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