504 SBXTINCT FISHES OF THE FAMILY GONORHYNCHID=. [ 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 distinctly 
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, however, 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; while the other 
fragmentary remains placed here are at least problematical. 
The three fishes thus briefly noticed are so closely similar to the 
recent Gonorhynchus 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 fresh- 
water 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 fish has large teeth on the pterygoid and hyoid bones. 
Secondly, their suboperculum 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 Gonorhynchid of France and Wyoming thus 
requires a distinctive generic name, and there are three from 
which to select, namely, Anormurus (Blainville, 1818), Sphenolepis 
(Agassiz, 1844), and Notogoneus (Cope, 1885). The first was too 
imperfectly defined for recognition, while the second is pre- 
occupied (Sphenolepis, Nees, 1834); Notogoneus may therefore be 
adopted as in the foregoing notes. 
EXPLANATION OF PLATE XVIII, 
Fig. 1. Notogoneus osculus ; right lateral aspect cf head and opercular appa- 
ratus.— Hocene; Wyoming, U.S.A. ag.,articulo-angular; d., dentary ; 
fr., frontal; hm., hyomandibular; mz., maxilla; op., operculum ; 
ot., otic region; p.op., preoperculum ; s., scales; s.op., suboperculum, 
[P. 7491.] 
Fig. 2. Ditto; three terminal vertebra and hypural of same specimen. 
Fig. 8. Notogoneus squamosseus; lelt lateral and partly superior aspect of im- 
perfect head and opercular apparatus, two-thirds nat. size. Upper 
Eocene; Aix-en-Provence. r., branchiostegal rays; 2, preorbital 
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: pmz., 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. 
