1182 



SCANDINAVIAN I-ISHES. 



Genus PETROMYZON. 



The (liphi/cercaJ caudal fin continuous ahorc with the itostcrior part of the dorsal. Anterior doifal jilate of the 

 mouth funrished otdij at each end irith an eterated tubercle or pointed tooth. 



As we have mentioned above, in tlie Lampreys 

 we cannot speak of real jaws or ja\\-teetli; but witiiin 

 the suctorial disk of adult Lam|H'eys are set several 

 horny, j>ointed teeth or terete protuberances, charac- 

 teristic of different genera and species, and to these 

 teeth it has been hitherto customar)- to give such names 

 as if they were set in real jaws. The oral aperture 

 is first surrounded, as we have seen, by an annular 

 cartilage (fig. 343, ami). This bears botli on its an- 

 terior (upper) and its posterior (lower) margin an hori- 

 zontal dental plate furnished with more or less pointed 

 teeth (fig. 3.52), which may be called respectively an- 

 terior teeth (at) and [losterior teeth (pf). On each side 

 of the annular cartilage there lie in the sucking-disk, 

 next the mouth, three small loose cartilages, each set 

 with 1 — 3 horny teeth (protuberances), which we entitle 

 the lateral teeth of the mouth {alt, mit, and ^)?0- Out- 

 side these the sucking-disk has within its fimbriated 

 margin a number of scattered teeth, arranged in rings 

 or in carved rows, suctorial teeth, as Gunther calls 

 them {ist and est). Within the mouth itself, between 

 the anterior and ]>osterior dental plates, appear the 

 lingual teeth, an anterior {ahi) and two posterior (^j/«) 

 curved dental plates, parallel to the posterior dental 

 plate of the mouth. It must be observed, however, 

 that when the tongue is protruded to its utmost extent 

 its posterior teeth project beyond the anterior ones, and 

 probably serve as the most po^verful I'asping organ of 

 the Lampreys. The dental character assigned above to 

 the genus Petromyzon is intended to express the fact 

 that the anterior dental plate of the moutli is neither 



bipartite, as in the Pacific genus Mordaria. with a 

 group of three teeth on each i)art, nor tridentate, as 

 in the genus Ichthyonujzon from the west coast of North 

 America". The other character given above diffei-en- 

 tiates all these genera fi'om Geotria, a Pacific genus, 

 with the caudal fin separated from the posterior dorsal. 

 A deep-sea genus, Bathymyzon, "with the suproral and 

 infroral plates or laminae destitute of odontoid tu- 

 bercles," was distinguished by Gill'' among the fishes 

 taken by the American fishing-schooner Albatross at a 

 depth of 520 fathoms within the area of the Gulf Stream 

 in lat. 49° N. He remarks, however, that the onlj' 

 species known {liathymyzon Bairdii) comes ^•ery near 

 to Petromyzon marinus. 



The species of the gciuis Petromyzon that belong 

 to the Scandinavian fauna are the same as are found 

 in other parts of Europe; but considering the variabi- 

 lity of form wjiich here asserts itself, we distinguisli 

 only the following: 



A: Anterior dental plate of the month 



so short that its two teeth stand close 



together — Subgenus Petromyzon Petro>niizo)i marinus. 

 B: Teeth on the crescent-like anterior 



dental plate distant from each other 



— Subg. Ammocoetes Petromiizon fluviatilis. 



a, var. viajor: the two dorsal fins 



more or less distinct- 

 ly divided from each 

 other — Petromyzon 

 fluvialilis. 



b, var. minor: the two dorsal iins 



more or less distinct- 

 ly confluent — Pe- 

 tromiizon brancliialis. 



" According to Jordan and Fordice :i imilinn tooth sometimes occurs on the anterior dental disk in Petvotiii/zon jiuviatiUs hnincliialis, 

 so that the genus lehthyoinyzon can hardly be retained. 

 *• Proc. U. S. Nat. Mue. 1883, p. 2.54. 



