| OCR Text |
Show 504 EXTINCT FISHES OF THE FAMILY GONOEHYNCH1DJ2. [Mar. 17 Formation and Locality. Upper Eocene (Gypsum); Montmartre Paris. This is a smaller and more slender species than either of the above, and the single specimen of it in the British Museum adds only one new fact to the description by Cuvier and Agassiz. The remains of the squamation above and behind the anal fin distinct.lv prove that the scales are identical with those of Gonorhynchus and Notogoneus, not only in form, but also in their characteristic posterior denticulation. It must, bouever, be remarked that the large head provisionally ascribed to this species by Agassiz is proved by its large den-tigerous mandible to belong to a distinct fish; uhile the other fragmentary remains placed here are at least problematical. The three fishes thus briefly noticed are so closely similar to the recent Govorhgnchus that it is difficult to realize their dating back to the earliest Tertiary period; but their interest becomes even greater when it is remembered that the three formations yielding their remains are proved by other associated fossils to be of freshwater origin. So far as known, indeed, these Eocene fishes can only be distinguished generically from Gonorhynchus by three characters. Firstly, they seem to be entirely toothless, whereas the recent tish has large teeth on the pterygoid and hyoid bones. Secondly, their subopercuium exhibits some deep clefts in its hinder border. Thirdly, their dorsal fin is in the middle of the back, while that of Gonorhynchus is much more remote. The extinct freshwater Gonorbynchid of France and Wyoming thus requires a distinctive generic name, and there are three from which to select, namely, Anormurus (Blainville, 1818), Sphenolepis (Agassiz, J844), and Notogoneus (Cope, 1885). The first was too imperfectly defined for recognition, while the second is preoccupied (Sphenolepis, Nees, 1834); Notogoneus may therefore be adopted as in the foregoing notes. EXPLANATION OF PLATE XVIII. Fig. 1. Notogoneus osculus; right lateral aspect of head and opercular apparatus.- Eocene; Wyoming, U.S.A. «^.,articulo-angular; d., dentary; fr., frontal; hm., hyomandibular; mx., maxilla; op., operculum; of., otic region ; P-op., preoperculuui; s., scales; s.op., subopercuium. [P. 7491.] Fig. 2. Ditto ; three terminal vertebrae and hypural of same specimen. Fig. 3. Notogoneus squamosseus; left lateral and partly superior aspect of imperfect bead and opercular apparatus, two-thirds nat. size. Upper Eocene; Aix-en-Provence. br., branchiostegal rays; x, preorbkal cheek-plate; other letters as above. [8052.] Fig. 4. Ditto; scale of caudal region of same specimen. Fig. 5. Gonorhynchus greyi; right mandibular ramus, upper jaw, and pre-orbital cheek-plate of recent fish: pmx., premaxilla; other letters as above. Unless otherwise stated the figures are of the natural size. The numbers in square brackets refer to the Register of the Geological Department, British Museum, where the fossils are preserved. |
