PALJiONISCXJS. GYROLEPIS, AND PYGOPTERUS. 573 



deutlich erkennbaren Wirbelsaule, an seiner, wenn auch in ver- 

 minderter Hdhe sich fast bis zur Schwanzflosse fortziehenden After- 

 flosse, wesshalb man ihm auch die Benennung Afterjlossenfisch geben 

 kann, nnd an der, der Afterflosse fast gerade gegeniiberstehenden 

 lliickenflosse." Again he remarks : — " Die Afterflosse beginnt bei 

 zwei Drittheil Lange des Bauches, dehnt sich anfangs stark in die 

 Hohe aus, wird dann aber schncll wieder niedrig, und setzt sich 

 nachher mit allmahlig vermindertcr Hohe bis in die INiahe der untern 

 Schwanzflosse fort. Die Riickenflosse steht der Afterflosse ziemlich 

 gerade gegeniiber, doch noch weiter nach vorn geriickt, so dass etwa 

 ihre Mitte dem Anfange der Afterflosse sich gegeniiber befindet, sie 

 steigt auch anfangs schnell und hoch empor und endigt nach hinten 

 durch eine sichel- oder halbmondf ormige Ausbiichtung "*. 



The definition of Pyyopterus given by M c Coy is as follows : — 



" Body large, elongate ovate ; fins very large, with fulcral scales, 

 anal fin of moderate depth and very long, dorsal of moderate length, 

 nearly opposite or a little in front of the anal fin ; ventrals small, 

 slightly in front of the middle of the body ; pectorals moderately 

 small, falcate caudal very large, deeply notched ; upper jaw a little 

 longer than the lower ; endoskeleton strong, vertebrae usually wider 

 than long ; scales proportionally rather small, rhomboidal, smooth, 

 and minutely punctured or diagonally striated, extending over the 

 pedicles of the fins, and particularly over the thick upper lobe of the 

 tail to the extremity, having a moderately wide articular margin, 

 sometimes prolonged at the upper angle, and having a medial internal 

 articular ridge which forms a prolongation from the middle of the 

 upper margin "f. 



What, therefore, the salient generic characters of Pygopterus are, 

 is perfectly clear from the foregoing extracts, which all refer to the 

 Permian species P. Humboldtii and P. mandibularis ; for even 

 Agassiz, though he enumerated several other species from the Car- 

 boniferous formation, made only the briefest possible reference to 

 their distinctive characters, deferring that description to a future 

 opportunity, which, unfortunately for fossil ichthyology, never 

 arrived. These two species, which, indeed, resemble each other ex- 

 ceedingly closely, must therefore be taken as typical of the genus. 

 It now remains for us to inquire whether the others named by 

 Agassiz sufficiently agree with them in structure to warrant their 

 retention under the same generic title. 



The species of " Pyyopterus " enumerated by Agassiz, in his 

 general list of Ganoids, are the following : — 



From the " Coal-formation.'' 



1. P. Bonnardi, Muse, near Autun. 



2. P. Buchlandi, Burdiehouse. 



3. P. lucius, Saarbriickcn. 



4. P. Jamesoni, Burdiehouse. 



5. P. Greenocl-ii, Newhaven. 



* 'Die Yerstcinerungcn des Mansfelder Kupferschiefers ' (Halle, 1840), 

 pp. 22-24. t * Palaeozoic Fossils.' 



From the Permian (Zechstein). 



G. P. Humboldtii. 



7. P. mandibularis. 



8. P. sculpt us. 



