OF THE AMBRICAJf PTERASPlDIAIf, PAL^ISPIS. 



555 



possible. The conical hollow was in that case the lodgment of the 

 motor muscle on whose decay its place was filled, as that of the 

 other soft parts, with mud. 



The resemblance of these ' fins ' to those of Huxley's Crosso- 

 pterygians was noted above, and I may add that two forms appear to 

 prevail, one broad and the other narrow. This difference may 

 indicate that more tban one pair belonged to the same individual 

 as pectorals and ventrals, or it may be of slighter import. 



Fig. 7 — Shield with '•Jtn ' lying by its side — in life-position ? 



A somewhat curious specimen which is in my possession gives us 

 a little more information concerning the organ above described. 

 It is at present quite unique, and was employed to illustrate the 

 lateral plates. By turning back to fig. 4 (p. 552) and closely 

 examining the lateral plate which is partly shown in its cast, 

 there may be seen in the very angle a small roundish object 

 looking extremely like what the base of such a fin would show if 

 preserved in place. I am unable to interpret it in any other way 

 than by regarding it as the actual inner extremity of an organ such 

 as I have above described. This specimen must therefore be 

 regarded as strongly confirming the opinion that we have here a real 

 lateral organ — one of a pair of fins, pectoral or ventral or the two 

 combined — whereby Palceaspis balanced itself in the water. Un- 

 fortunately I do not possess the cast of this specimen, which might 

 have afforded yet more testimony in the same direction, and the 



Q.J.G.S. No. 192. 2q 



