1044 



SCANDINAVIAN KISIIES. 



I 



only two types survive, iiiliMl)it;uits uf the tropical re- 

 gions of Africa (the Bichir, J'olijptpius) and America 

 (the J3onj' Pikes, Lepidosfeus). Lutken" restricted the 

 scope of the Ganoids to tlic iMst-nientioned division 

 (MCller's Holostei), but I'anged theiu as well as the 

 Sturgeon-fishes (MCllicu's Chonclrostei) in the categor)- 

 of distinct subdivisions among the Teleostean Physostoms. 

 The free gill-arches alone, with the branchial la- 

 mellaj projecting beyond their free, outer (convex) mar- 

 gin, are enough to distinguish the Sturgeon-fishes from 

 tiie true cartilaginous fishes and approximate them to 

 the Teleosts, with which they are also allied by several 

 other points in their organization, e. g. the covering of 

 the liead witli nienil)rane-ljones tiiat distinctly represent 

 the several component l)ones of the Teleosteous cranium, 

 and the structure of the generative organs. Their in- 

 clusion witliin the (jrder of tiie Teleosts is indeed for- 

 bidden not only by the above-mentioned chanicters 

 (rinasmfi and coni(s), but also by the structure of the 

 extremities, wherein the Sturgeon-fishes have preserved 

 a great portion of the |jrimordial cartilaginous radialia, 

 as well as l)y the undi\ided chondroci'aniuin and the very 



partially transformed notochord. But LCtken is, bevond 

 doubt, fully justified in his o])inion that the Sturgeon- 

 fishes have far more in common with the Teleosts than 

 witii tlie true cartilaginous fishes. Dodeuleix'' too com- 

 bined them together with the Teleosts and the true 

 tianoids into an order, Teleostoini, cliaracterized l)^• tlie 

 completely ossified skeleton or at least by membrane- 

 bones on the head and shoulder-girdle, bv the free 

 (joined to the cranium bv articulations, sutures, or 

 ligaments) hyomandibular and palatoquadrate arches', 

 and by the unarmoured pectoral fins'. Among the 

 Teleostoins they are distinguished by their fully hetero- 

 cercal caudal fin, with the tip of the spinal column ex- 

 tending (piite or nearlv to the end of tlie upper caurlal 

 lolie, and by their unilaterally raved' paired fins. In 

 DoDEHLEiN they rank, with these characters, us a sub- 

 order (Fleferocerci). In the Scandina\i;ni fauna, winch 

 contains neither Lung-fishes (T)ip)i(i}) nor (ianoids, it 

 may suffice to have drawn attention to the relation of 

 the Sturgeon-fishes to the Teleosts and the true carti- 

 laginous fishes, which is adequately expressed by MuL- 

 LEKS interpretation of then\ as a distinct ordei'. 



Fam. ACIPENSERlDiE. 



Bodji fusiform, with fire rows of large osseous hucklers. Four barhels in a transverse roir on the under surface 

 of the s)ioiif, in front of the profriisile month. No hranchioster/al rai/s. 



In modern times the ("hondrosteous order contains 

 oidy two families, one of which, the American and 

 Chinese Polyodontida, with almost or quite naked body 

 and without barbels, is ]u'incipally distinguished by its 

 conq)ai'atively large moutli, o]i('n I'ven laterally (on the 

 sides of the head), and with upper jaw incapable of 

 protrusion, the anterior exti'cniitv of tlie palatine arch 

 being firmly united by ligaments to the under surface 

 of the skull. Another important difference is that the 

 I'ohiodoiitidte are without psendobranchiu', those of the 

 Sturgeons being exceedingly well developed, even func- 

 tional as gills, with at least superiorly free branchial 

 lamelliE, on the inside of the opcrcula. 



< )n ii])eiiiiig tlie pharvngeal and bi'anchial cavities 

 of a Sturgeon, the most striking difference from all 

 the Teleosts meets us in the roof of the palate. This 

 (fig. 284, mx — mpt) is a continuous, convex disk, with 

 free margins lioth in front and beliind, and capable, 

 together with the toothless jaws and fleshy, tumid lips, 

 of protraction forwards and downwards and of retrac- 

 tion. On each side of the deej) fold that hangs, covered 

 with the thick mucous membrane of the phaiynx, be- 

 tween the free hind margin of the palatine roof and 

 the under surface of the skull (jiarasphenoid bone) or 

 jiosterior, fixed palatine roof with its continuation, the 

 roof of the pharvnx, we find an a]icrture. This hole 



" Om Ganoideriais lier/riendsniiii/ oij Inddeling, Vid. Meildel. Nntiirli. For. Kblivu, 1868, scp. 



'' Stkinmann and D6derlein, Elcinenle dcr Puldontologie, p)i. 540 and 5.51;. 



' As opposed to the Lung-fislics. 



'' As opposed to tlie priiiievnl iuid extinct Placoderiin (Pterich/hi/s, Ce/ilialaspi.'^, etc.). 



'■ Not loliate, or but sli^litly so, in contrast to tlie strongly lobate fins of tlie so-called Crossopteri/i/ii 



