No. I.] MORPHOLOGY (OF “CLADOSELACHE: 105 
stoutness in different regions. Those that have fused together 
to form the circum-orbital plates have already been commented 
upon by Jaekel, whose figure, slightly modified by the writer, 
is here reproduced (Fig. 5). An entire ring of derm-plates as 
shown in a more perfectly preserved specimen (C. fylerz) is 
also figured (Fig. 6). Their Acanthodian characters have been 
noted. 
Dermal investiture of the fins, as already seen, is as yet 
specialized in the development of only the most minute rays. 
These appear to be intercalated between the primitive 
cartilage rays. In the pectorals they suggest from their 
extreme fineness of character, the slightest plaitings of super- 
ficial derm layer (Fig. 1). In the ventrals, however, they 
are not to ‘be positively defined. Those of the tail are 
clearly marked, and have evidently been of a degree of use- 
fulness consequent, perhaps, of the absence of cartilaginous 
supports in the upper lobe. They certainly agree in arrange- 
ment and direction with the firm dermal supports of the upper 
lobe in modern sharks. It is of especial interest that in the 
paired fins of this ancient form the superficial rays are inter- 
calated, and not joined on to the endoskelal part in a 
fringing line; it is thus suggested that the protrusion of 
these parts from between the cartilages, which gave them 
direction as well as support, was the origin of the dermal fin. 
Where greater rigidity combined with hghtness was required, 
as in the outer posterior border of fin, the cartilaginous 
radials were obliged to resort to processes of forking, splitting 
and interwedging their pointed tips, devices which could not 
long remain in competition with the dermal ridges which now 
became acquired secondarily. The latter have, in paired fins, 
developed on the same lines as the older structure, have spread 
between them, and usurping their functions, have caused their 
degeneration. 
Of lateral line nothing is determinable in specimens that are 
to be positively referred to the type genus. A portion of a 
shark from the locality in which C/adoselache was found shows 
clearly a lateral line, which is figured (Fig. 7), although but 
doubtfully referred to this form. It is especially interesting 
