56 WELLBURX : ox THE GENUS MEGALICHTHYS, AGASSIZ. 
Polypterus, the skeleton being more like that found in Ceratodus^ 
with the difference that the basal cartilage {Metapterygium) is 
somewhat shortened, the radials on its anterior border atrophied, 
tliose on the posterior border enlarged, and the cartilage seen 
along the post axial border of the fin being elongated to form 
a propterygium, this giving a structure similar to that shown 
in Fig. A, PL XVII. 
Prof. Cope gives a section (Proc. W. S. Natl. Museum, 
Vol. XIV., p. 457) of the lobe of the pectoral fin of M. nitidus 
Cope, which shows a well-marked metapterygium, with radials 
springing from its tip and outer or posterior edge. 
The dermal fin rays form a fringe around the lobe, they are 
closely articulated, the articulations being rather longer than 
broad, and covered with ganoine similar to that on the scales, 
distally they increase in number by dichotomisation and become 
much finer. The anterior rays are much more robust than those 
situated further back. 
Ventral fins. — The fins are abdominal and their position and 
character are well shown in a fish in the Hugh Millar Collection 
in the Science and Art Museum, Edinburgh. Their basal 
characters are also well shown in the Leeds fish, the right one 
being the better preserved. 
The fin is obtusely lobate, the base being invested with large 
scales which are continued along the internal or post -axial 
border; along the outer or preaxial border is a shorter series of 
large scales Avhich meet the others (post-axial) at an acute angle. 
The space between these rows is occupied by a close series of 
smaller scales arranged in many parallel rows. Here, again, the 
external characters probably indicate the internal skeleton which 
is thus described by Prof. Miall : " The larger scales conceal a 
strong pro- and a metapterygium, whilst the smaller scales cover 
numerous radials which spring from the outer edge of the 
metapterygium. " 
The section of the basal portion of this fin given by Cope 
(op. cit.) goes to prove that a strong, well-marked axial rod or 
metapterygium was present, with well-marked radials springing 
