'504 EXTINCT FISHES OF THE FAMILY GONOEHYNOHID-S!. [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 Kn distinctly 

 prove that the scales are identical with those of Oonorhynchns 

 and Notoyoneus, not only in form, but also in their characteristic 

 posterior denticulation. 



It must, however, be remarked that the large head provisionally 

 ascribed to this 8i)ecies by Agassiz is proved by its large den- 

 tigerous mandible to belong to a distinct tish ; « hile the other 

 fragmentary remains placed here are at least problematical. 



Tho three fishes thus briefly noticed are so closely similar to the 

 recent Oonorhynchns that it is dillicult to realize their dating back 

 to the earliest Teriiary 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 fresh- 

 water origin. So far as known, indeed, these Eocene fishes can 

 only be distinguished generically from Gonorhynchus by three 

 cluiracters. Firstlv, they seem to be entirely toothless, whereas 

 the recent fish has large teeth on the pterygoid and hyoid boues. 

 Secondly, their suboperculum exhibits S(mie deep ctlefts in its 

 hinder border. Thirdly, their dorsal flu is iu the middle of the 

 back, while that of Oonorhynchus is much more remote. The 

 extinct freshwater Gonorhynchid of France and Wyoming thus 

 reuuires a distinctive generic name, and there are three from 

 which to select, namely, Anormur-us (Blainville, 1818), S^ihenolejiis 

 (Agassiz, 1844), and Notoijoneus (Cope, l«8o). The first was too 

 imperfectly defined for recognition, while the second is pre- 

 occupied (Sphennlepis, Nees, 1834); Notogoneus may therefore be 

 adopted as iu the foregoing notes. 



EXPLANATION OF PLATE XVIIL 



Fig. 1. Kofogoneus osculus ; right lateral aspect of head and opercular appa- 

 ratus. — Eiicene; Wyoming, U.S.A. a^.,articulo-angulur ; d, dentaiy; 

 fr., frontal ; hm., hyomandibular ; mx., maxilla ; op., operculum ; 

 «)■., otic region ; ^.op., preoperculuui ; s., scales; s.op., subopercuhuii, 

 [P. 7491.] 



Pig. 2. Ditto ; three terminal vertebra; and hypural of same specimen. 



fig. 3. Moiogoneus squamosseus ; lelt lateral and partly superior aspect of im- 

 perfect bead and ojiercular apparatus, two-tliiids nat. size. Upper 

 Eocene ; Aix-en-Provenee. br., branehiostegal ruys ; a', preorbital 

 cheek-plate; other letters as above. [8052.] 



Fig. 4. Ditto; scale of caudal region of same specimen. 



Fig. 5. Gonorhynchus grei/i; right mandibular ramus, upper jaw, and pre- 

 orbital cbeek-plute 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. 



