530 Prof. B. S. Traquair — On a new Carboniferous Fish. 



of the caudal. The dorsal fin commences low in front, but becomes 

 deep and broad, as the form of the body narrows towards the tail. 

 As regards the form" of the tail, and the relations and configuration 

 of the dorsal fin behind, Professor Huxley's views, at the time he 

 wrote his descriptions, were, that the dorsal terminated posteriorly 

 in an almost vertically truncated extremity, beyond which the noto- 

 chord was continued for some distance. The upper lobe of the 

 caudal seemed to be obsolete, while, on the other hand, he could 

 trace the lower lobe, commencing immediately behind the anal, to 

 near the extreme end of the body.^ Subsequently obtained material, 

 however, shows that the appearances which justified so eminent a 

 palaeontologist in adopting the above-mentioned views were due to 

 defective preservation of the specimens at his disposal, and that the 

 dorsal fin was, as in the recent Lepidosiren and Ceratodus, continued, 

 as a dorso-caudal, to the very extremity of the body, which con- 

 dition I have endeavoured to express in the subjoined woodcut, re- 

 presenting a restored outline of the fish. I may mention that Prof. 



Eestored outline of Fhaneropleuron Andersoni. 



Huxley has expressed to me his entire concurrence in this view. 

 The tail of Plianeropleuron is, then, beautifully diphycercal, a slight 

 tendency to the heterocercal form being, however, shown by a very 

 constant, though slight, upward curvature of the caudal extremity of 

 the body. 



I am also in a position to give a few additional details regarding 

 the structure of the head, though unfortunately our knowledge on 

 this point still remains very imperfect. In general configuration 

 the head must have resembled much that of Ceratodus Forsteri, 

 being considerably flattened above, while the high occipital region 

 slopes ofi" downwards and forwards to the bluntly-pointed muzzle. 

 Internally, the cranium seems to have been very extensively carti- 

 laginous, as I have seen no trace of any ossifications of its base or 

 side-walls, but above it was protected by a buckler formed of a 

 great many osseous plates firmly articulated together by suture, 

 though none of the specimens I have seen are sufficiently perfect to 

 enable one to map out completely their number and arrangement. 

 However, in two of the specimens in the St. Andrew's Museum, 

 three plates, one median and two lateral, may be very distinctly 

 made out, forming the posterior or nuchal margin of the cranial 

 shield, and corresponding to the three similar plates in GlyptolcBmus. 

 In front of the median plate are two elongated parietals, while on 

 each side of it, and articulating also with the posterior external 



1 Mem. Geol. Survey, Decade X., p. 49. Also in Anderson's " Dura Den," p. 67. 



