1887.] 



PAIRED FINS OF CERATODUS. 



Schneider 

 Observed . 



Schneider . 

 Observed 



Pectoral Jin. 

 Postaxial. 

 Seg. ii. iii. iv. 

 .522 

 . 3-5 1-9 1-6 



Pelvic Jin. 

 Postaxial. 

 Seg. ii. 

 . 1 

 . 2-1 



V. 



1 

 1-3 



Preaxial. 

 ii. 

 1 

 1 



Preaxial. 

 ii. 

 2 

 2-5 



Further comment upon the pectoral member may be deferred until 

 later. Concerning the ten pelvic fins examined by me, I may add 

 that in eight the second mesomere bore preaxially two parameres 

 (figs. 3& 7); in a ninth three; in a tenth four. In most cases 

 two postaxial rays were present (fig. 7). One fin, interesting beyond 

 this, bore (fig. 2, right hand, as drawn) preaxially two rays, post- 

 asially four, that being a precise reversal in duplicate of the condi- 

 tion observed by Schneider. In no case have I observed the distri- 

 bution recorded by him. 



The parameres of all the fins alluded to were, for the most part, 

 rod-like and segmented ; but in not a few instances they were 

 branched or otherwise modified {cj. figs. 1, 5, 7). Reflection upon the 

 facts recorded concerning them, to say the least, shakes our trust 

 in the supposed regularity of their distribution. That, however, 

 can no longer be asserted, in view of the truly remarkable condition 

 of one pair of fins, which belonged to a fish in all respects normal 

 and healthy (fig. 2). Giinther first directed attention to the sickle- 

 shaped contour of the Ceratodus fin, and all subsequent observers 

 are agreed as to the asymmetry of its two lobes. Schneider states 

 (23, p. 521) : — " das zweite Glied des Hauptstrahls zerfallt durch 

 eine Langsgrube in zwei Stiicke. Das eine Stiick behiilt die Richtung 

 des Hauptstrahls, das andere Stiick divergirt mit demseli)en und 

 zwar bei der Biustflosse dorsalwarts, bei der Bauchflosse ventral- 

 warts." And further, " Die Seitenstrahlen der dorsalen Hiilfte der 

 einenFlosseentsprechen derjenigen der ventralenHalfte derauderen." 

 A cursory glance at the pair of fins now under consideration (fig. 2 ') is 

 sufficient to show how erroneous is this deduction. That Schneider 

 has accurately represented the facts for the animals at his disposal, 

 I have no doubt ; but that his conclusions are incapable of a wider 

 application is here proven. 



' I was at one time under the impression, from an examination of DavidofFs 

 figures (7, pi. 9. figs. 6 & 7), that he had been dealing with a similar pair of 

 fins ; but I am no longer in doubt. His drawing of the fin-skeleton of fig. 7 is 

 not in accord with the description given, as regards the pelvis and basal 

 mesomere. He, moreover, states emphatically (p. 127), " die Zahl der ventralen 

 resp. medialen Eeihe [referring to the parameres] entspricht genau der Zahl 

 der Gliedstiicke des Stammes, wahrend diejenige der dorsalen resp. lateralea 

 Reihe fust genau um das Doppelte grosser ist ? " 



