57 2 kamsay h. traquair ox amblyrxerus, 



Pygopterus. 



The definition of Pygopterus given by Agassiz in the " Tableau 

 Synoptique " is as follows : — 



" A. tres-allongee : D. opposee a Tintervalle entre l'A. et les V. 

 La machoire superieure deborde l'inferieure. De petits rayons le 

 long des rayons exterieurs des nageoires." 



Further on in the volume the characters of the genus are indi- 

 cated more in detail. The large size of the fins, especially of the 

 heterocercal and deeply cleft caudal, is noticed, the paired fins being 

 less developed ; also the pointed conical teeth, the comparatively 

 small size of the rhomboidal scales, and the well -developed internal 

 skeleton. But it is on the form of the anal fin that the greatest 

 stress is laid : — " Mais ce qui caracterise plus particulierement les 

 Pygopterus, c'est qu'a cette caudale inequilobe se joint une anale 

 fort longue qui garnit le bord inferieur du corps sur une grande 

 etendue." The dorsal is still stated to be placed opposite the inter- 

 space between the ventrals and the anal, but " de maniere a etre 

 plus rapprochee de cette derniere/' In his description of P. man- 

 dibularis, however, Agassiz states that in it the anal is more directly 

 opposed to the dorsal than in P. Humboldtii. 



The restored outline of Pygopterus given in the Atlas to the 

 ' Poissons Possiles ' (vol. i. tab. B. fig. 3) displays, however, the 

 same faults as the accompanying restorations of Palceoniscus, Ambly- 

 pterus, &c, viz. a want of acquaintance with the structure of the 

 head, besides considerable inaccuracies as to the general form of the 

 body and fins. Had Agassiz been acquainted with the cranial 

 osteology of the Palaeoniscidae, it is, indeed, impossible to conceive 

 that on the sole ground of the possession of large laniary teeth, he 

 could have separated Pygopterus and Acrolepis, as " SauroVdes," 

 from their natural allies Palceoniscus and Amblypterus, a precisely 

 similar dentition existing, as has been subsequently shown, in several 

 of the species which he referred to the two latter genera. 



By Quenstedt a peculiarity of Pygopterus, certainly of generic 

 value, is noticed, which seems to have escaped the attention of 

 Agassiz, viz. the non- articulation of the principal rays of the pectoral 

 fin. As he says : — " Die grossen ungegliederten Strahlen der Brust- 

 flossen errinern an Pachycormus" The position of the dorsal fin is 

 also more correctly indicated by Quenstedt, according to whom it 

 stands, " weit hinter der Bauchflosse iiber der vordern Halfte der 

 langen Afterflosse," though he might also have mentioned that it 

 commences in front of the latter. He also gives a figure of some of 

 the bones of the head (operculum, maxilla, mandible, branchiostegal 

 rays), in which the essential agreement of these in form and 

 arrangement with the corresponding bones in Palceoniscus is clearly 

 shown *. 



The peculiar form of the anal fin is also emphasized by Germar, 

 by whom the position of the dorsal fin is correctly stated in the 

 following words : — " Man erkennt diesen Fisch sehr leicht an den 



* 'Handbueh der Petrefaotenkunde/ 2nd ed. (I8fi7). p. 269, pi. 21. fig. 4. 



