woodward: fossil STURCEON of the WHlTIiY LIAS. I05 



exhibit the minute superficial asperities so characteristic of the 

 pectoral fin of Choudrosteus. The rays of the other fins appear to be 

 all closely jointed, and a large portion of the tail-fin, displaying this 

 character, is shown, of one-third the natural size, in fig. 6. These 

 caudal fin-rays are unjointed for a short distance at their inserted 

 end, but they soon become crossed by closely-arranged sutures, and 

 nearer their extremities they bifurcate once or twice. 



Fig. 6. C.iudal fin-rays of Gyrosttiis mirabilis; one-third natural size. 



No scales or dermal plates are known, and the body was thus 

 probably naked, as proved to be in CJiondrosteus. Indeed, the 

 oblong .scales found to invest the unsymmetrical upper lobe of the 

 tail in all known Sturgeons, recent and fossil, have not yet been 

 recognised ; but the upper margin of the tail is bordered in the 

 usual manner by a row of great saddle-shaped, imbricating scutes— 

 a feature well shown in the restoration of Choudrosteus (fig. 7). 



April 1890. 



