598 OR RAMSAY H. TRAQUATR ON THELODUS PAGET. 



Squalidse or Sharks, and says of it and of Pander's Pachylepis, that they " wahrschein- 

 lich zu Onchus gehoren."* 



Mr Smith Woodward in his Catalogue, part ii. (1891), p. 156, places the Ccelo- 

 lepidse as " Incertse sedis" at the end of the Elasmobranchii. Like Pander, Mr Woon- 

 WARD makes no remark as to these scales having belonged to the same fishes which 

 bore the Onchus spines. 



Professor J. V. Rohon, in his second paper on the " Upper Silurian Fishes of Oescl." 

 published in 1893,t adopts Pander's Ccelolepidse, which he places in the sub-class 

 Selachii, order Plagiostomi, and sub-order Squaloidei. They are, he says, " ausgcstor- 

 bene Selachier, deren Haut mit Placoidschuppen bedeckt war," adding also that " zn 

 diesen Schuppen gehoren wahrscheinlich auch Zahne und Flossenstacheln (Monophu- 

 rodus, Onchus)." Rohon, in fact, adopts M 'Coy's opinion, that the Thelodus scales 

 and Onchus spines belonged together, adding also the small teeth named Monof)leur<"i".< 

 by Pander, as probably appertaining to the same group of fishes. He also describes 

 minutely the microscopic structure of the Coelolepid scales, comparing them in this 

 respect with those of the extinct Acanthodei, and of the living Selachii. His conclu- 

 sion is that the Coelolepid scales are genuine " Placoidschuppen," but, as they in many 

 respects show a simpler condition of histological structure, they must be regarded as 

 placoid scales in a lower stage of development. 



We have seen that Zittel, in 1887, placed the Ccelolepidse among the Squalicla), 

 but in 1895 he is more disposed to refer them to the Acanthodei. Treating of the last- 

 named group, he says : — 



" Die grosse Uebereinstimmung der CZi'mataMs-stacheln mit gewissen als Onchvs be- 

 zeichneten Ichthyodorulithen lasst es uberaus wahrscheinlich erscheinen dass wenigstens eiu 

 Theil der letztgenannten im oberen Silur und Devon verbreitcten Reste von Acanthodiden 

 hcrruihren. Hochst wahrscheinlich gehoren auch die vierseitigen Chagrinschuppen 

 welche von Agassiz unter dem Namen Thelodus aus dem obern Silur von England, von 

 Pander unter der Bezeichnung Ccelolepis, Thelolepis, Pachylepis, und Nostolepis aus 

 dem oberen Silur von Oesel beschrieben wurden." \ 



To sum up, then, the current opinions concerning the Ccelolepidae, it would seem 

 that these scales are now looked upon either as incertce sedis, or as having belonged to 

 true Squall or to Acanthodei, and that the notion is also entertained by many thai the 

 defensive spines known as Onchus formed part of the dermal armature of the same 

 creatures. 



It is the object of this paper to show, by means of a re-examination of the Lower Old 

 Red Fish called by Powrie Cephalopterus Pagei, that, though probably of Elasmobranch 

 ancestry, the Ccelolepidai cannot be classed either as Squali or as Acanthodei, and thai ii 

 is not among them that the ancient possessors of the Onchus spines must be looked for. 



* Handbuch der Palcvontolotjie (Palujozoologie), vol. iii. p. 64. 



t Die Obersilurischen Fischa von Oesel, ii. Theil ; Mem. Acad.. Imp. Sc. de St Petersbourt/, t. xli., No. 5, 1S93. 



X Qrundxugi •'■> Palceontologie, Munich and Leipzig, 1895, p. 530, 



