No. I.] MORPHOLOGY OF CLADOSELACHE. 103 
the tip of the chord be upturned, the (derm) rays absent, and a 
stouter outgrowth of the cartilaginous radials. 
Among ancient forms all stages of gradation from hetero- 
cercy to diphycercy might well be illustrated in the ancient 
Crossopterygians, Holoptychius, Osteolepis, Gyroptychius, Gly- 
tolaemus. Further degeneration in these forms might result 
in typical gephyrocercal types, whose transitional stages would 
be represented in Coelacanthids, ¢.g., Coelacanthus, Undina, 
Diplurus, Macropoma. From the tail type of Cladoselache 
diphycercy, as shown in Xenacanthus, might readily have 
taken its origin ; it would have required merely the continu- 
ation posteriorly of the hypural rays and a gradual down- 
turning or degeneration of the tip of the chord, —a condition 
specialized to environment, which among recent forms is 
clearly evolved in the case of the eel. 
This view as to the derived character of what is accepted as 
diphycercy certainly assists not a little im closening phylo- 
genetic ties. It adds further evidence for the nearing of 
Dipnoid as well as of Crossopterygian forms to the stem 
ancestral of Xenacanthids. It aids, moreover, in the com- 
parison of Xenacanthids with more ancient and more 
generalized Elasmobranchs. 
THE UNPAIRED FINs. 
The structure of the unpaired fins of Cladoselache would 
naturally be expected to prove of great morphological interest. 
The present material, unfortunately, does not permit any satis- 
factory determinations. In a single specimen is preserved a 
detached fin of Cladoselache kepleri (?) which is entirely different 
in type from pectoral or ventral, and might, perhaps, be 
regarded as dorsal. 
The specimen (Fig. 4) presents nine fin rays (radials) in a 
graded series, of which the foremost is the shortest. In this 
region, as in the other fins, the rays are concentrating and fusing, 
are most erect, perhaps may even have inclined slightly forward. 
The caudad rays are most inclined, abruptly tapering and 
become distinctly hollow in their basal half. It is interesting 
that each ray at its distal hinder edge has split off a bridge- 
