602 DR RAMSAY H. TRAQUAIR ON THELODUS PAGEI. 



The recognition of Powrie's " Cephalopterus" Pagei as a veritable species of the 

 genns Thelodus docs indeed throw quite a new light upon the ancient family of 

 Coelolepidse. 



In the first place it absolutely disposes of the supposition that the fin-spines 

 known as Onchus, Agassiz, or the teeth known as Monopleurodus, Pander, and Ancis- 

 trodus, Rohon, had anything to do with this family. Tlielodus Pagei shows neither 

 teeth nor fin-spines, and in these particulars the Coelolepidse, to be described in ray 

 forthcoming "Report" on the Upper Silurian fishes collected by the Geological Survey 

 of Scotland in Lanarkshire, perfectly agree. The general form of the body likewise, 

 as well as the absence of recognisable jaws and teeth are features decidedly against 

 the retention of Thelodus in the order Selachii at all. 



In the second place, these specimens render it equally certain that Thelodits is 

 not referable to the Acanthodei. 



In my next paper I shall endeavour to show that a series of forms connects Thelodus 

 with the Heterostracous division of the Ostracodermi, and that the Ccelolepidyj in 

 fact belong to that order. Nevertheless, the nature of their dermal covering clearly 

 points to an Elasmobranch affinity, and to the idea that through them the Hetero- 

 straci have had a common origin with the primitive Elasmobranchs. # 



EXPLANATION OF PLATE. 



Figs. 2-8 enlarged eight diameters. 



Fig. 1. Thelodus Pagei (Powrie) ; reduced one-third. From the Lower Old Red Sandstone, Turin Hill, 

 Forfarshire. (Powrie Collection, Edinburgh Museum of Science and Art.) 



Fig. 2. Outer surface of scales from near the front ; magnified eight diameters. 



Fig. 3. Under surface of a scale, from a wax impression, showing a basal opening of considerable size. 



Fig. 4. A scale broken through horizontally, showing the internal pulp cavity. 



Fig. 5. Three scales from a patch of shagreen belonging to Thelodus Pagei but from Canterland, Kin- 

 cardineshire. The two lower scales seen from the side ; the upper one, from below. (Powrie Collection.) 



Fig. 6. Four scales from the same patch seen from below ; in two the basal opening is very small ; in 

 two it is apparently absent. 



Fig. 7. Scale from the same patch, broken through horizontally, showing the pulp cavity reduced to a 

 narrow chink. 



Fig. 8. Scale from the same patch, seen from below, showing a small basal opening. 



* It may, however, here be noted that Dr 0. M. Reis of Munich has already expressed the opinion regarding the 

 Pteraspidffi, the only family hitherto by common consent included in the Heteroslraci, that they, along with the 

 Psammoateidffi, "eine einheitliche Degenerationsgruppe der Elasmobranchier bilden," Geoynostisclie Jahreshefte, vi. p 64 

 See also tin- Same author in Sciiwalbe's Murpliologische Arbeiten, vi. p. 213. 



