58 
WELLBURN I ON THE GENUS MEGALICIITHYS, AGASSIZ. 
Characters. — On each side of the lobe is a large "basal" 
scale, the function of which seems doubtful. The dermal rays 
are of similar character and arrangement to that of the pectoral 
fin. 
Internal Skeleton consisted of a single club-shaped axonost, 
its broad basal portion bearing several rod-like baseosts, which 
were jointed at intervals and bifurcating, the more anterior ones 
being the most robust. The dermal rays are much more numerous 
than the supporting ossicles, and were of a character similar to 
those of the pectoral fin. 
Dorsal fiiis. — These fins were lobate, the lobe being more 
acute than that of the paired fins, the posterior fin is more 
strongly developed than the anterior, the dermal rays of both 
fins are similar in nature to those of the other fins, and the 
supporting skeleton is similar to that of the anal. 
Note. — A specimen in the British Museum (No. 38,007) 
shows that the supporting (or internal) skeleton of the unpaired 
fins was of a, similar nature to that described above. 
Caudal (PI. XVI. and PI. XVII., Fig. H.) The struc- 
ture (superficial) of this fin is well shown in several specimens 
in the Science and Art Museum, Edinburgh ; Lister Collection, 
Brighouse ; and Owens College, Manchester. The fin is inter- 
mediate in type between the diphycercal and heterocercal stages, 
and in general form reminds one of that of Tristichapterus, as 
pointed out by Dr. Traquair. 
The rays arise from both the upper and lower margins of 
the body prolongation, those of the lower side commencing in 
advance of those of the upper (see PI. XVI.). After the com- 
mencement of the rays the upper margin of the body slopes a 
little downwards, whilst the lower one first slopes somewhat 
rapidly upwards and backwards, then more gradually to meet 
the upper in a fine point, which is finally lost among the dermal 
rays, the scaly covering being continued to this point (PI. XVI., 
and PI. XVII., Fig. H). 
