614 MB. J. W. DAVIS ON CHONDKOSTEUS ACIPENSEKOIDES. 



beyond which it bifurcates, possibly to support the two ventral fins. 

 The bone is opposite to the anterior insertion of the dorsal fin. 

 The anal fin is not represented. 



The caudal fin is very large, and a most powerful organ of 

 propulsion. The upper lobe, as in the recent Sturgeon, is the 

 longer of the two, and its extremity is more pointed than that of 

 the lower one. The length of the upper lobe is 12*0 inches, that of 

 the lower 10*5 inches, and the terminations of the two are 13*0 inches 

 apart. Along the median portion of the upper lobe there is a series 

 of dermal scales or scutes ; at the basal part of the tail they cover 

 about an inch in breadth and extend almost to the termination of 

 the tail, gradually diminishing in area until they end in a point. 

 The scales at the base of the tail are of an elongated oval form ; 

 posteriorly they are greatly elongated and assume a rod-like form 

 pointed at each end. The upper external margin of the fin is 

 formed of a series of large, sigmoidally-curved, imbricating, fulcral 

 scales. Those attached immediately behind the pedicle of the tail 

 are about 1*0 inch in length, 0*2 inch in thickness in the middle ; 

 the basal and distal extremities are somewhat spatulate and thin. 

 Succeeding scales become more attenuated, and midway their length 

 has increased to 2*5 inches, with a medium thickness of 0*1 inch; 

 thence to the end they diminish both in length and thickness. 

 The strong basal fulcral scales are directly supported by a series of 

 short but thick neurapophyses. The latter do not appear to extend 

 more than two inches beyond the base of the tail. The lower lobe 

 of the tail is supported by haemapophyses of larger size and more 

 solid construction than the neurapophyses ; they are expanded at 

 the base, and have evidently been firmly attached to a powerful 

 vertebral axis. The latter was entirely cartilaginous and has 

 disappeared. The hsemapophyses can be distinguished a distance 

 of six inches from the base of the tail ; they gradually diminish 

 in length, but become broader and spatulate as they approach the 

 termination of the vertebral column. Attached to the hsemapo- 

 physes there is a long series of interhsemal bones, which form the 

 base of attachment for the rays of the fin. The latter are strong 

 and jointed from the base. A few short rudimentary rays are 

 followed by others which extend to the extremity of the lobe; 

 they are divided towards the extremity of each ray, the divided 

 portions again bifurcating until the external margin of the fin has 

 assumed a more or less filamentous condition. The rays decrease 

 in length and thickness as they are successively attached to the fin, 

 extending quite to the extremity of the upper lobe. Prom the 

 base to a point halfway towards the termination of the upper lobe 

 72 rays may be counted; beyond this point there are many others, 

 but the actual number is not easy to determine. 



The specimen of Chondrosteus described in the preceding pages 

 is nearly twice the length of those described by Sir Philip Egerton 

 (excluding C.pachyurus, which is only mentioned incidentally), whilst 

 the depth of the body, taken in front of the dorsal fin, is 6 inches, 

 the same as that of C. acipenseroides, so that this species approaches 



