MUSEUM OF COMPARATIVE ZOOLOGY. 15 
The basipterygium of the ventral is elongate and triangular, the iliac 
ridge being continued along its upper side. At its extremity there is a 
series of three radials. The majority of the radials are in three series, 
but some of the posterior form a single one. ‘Thirteen radials articulate 
with the side of the basipterygium. 
The Cartilages of the Anal Fin. 
Plate XIII. 5-3. 
These cartilages occupy an extent of three fourths of an inch at the 
widest by about seven inches in length. The fin itself is less than half 
an inch longer. The band of cartilages is widest forward and tapers 
toward the tail; it is widely separated from the hemapophyses. The 
radials are thin, and have not a great deal of rigidity. Segmentation 
has been very irregular in its operation: in the lower half of the band, 
the radials are directed backward in the usual manner ; in the upper 
half, nearer the vertebrae, a few segments agree with the former, but 
the majority are directed obliquely forward. The directions of the lines 
of separation in either case are those separating the interneurals and 
the neurapophyses, and are probably determined by similar causes, — 
movements of the body in particular directions, or the directions of 
the forces exerted by the muscles. 
The Cartilages of the Dorsal Fin. 
Plate XIII. Fig. a-a. 
The series of cartilages in the base of the dorsal is three fourths of an 
inch in width by four and three fourths inches in length. It is widest 
backward and tapers gradually in front. It is not near the vertebree ; 
its only connection with the latter is by membrane. That portion of 
the base extending in front of the fin has its radials directed obliquely 
forward ; the vart beneath the fin, though irregular, has them directed 
backward. *” 
The great extent of the band compared with the size of the fin, and 
the manner in which it dwindles toward the front, taken in connection 
with the fact of the continuation of the peculiar scales of the fin border 
some two inches in front of the cartilages, show that in ancestral forms 
of this animal the dorsal fin was much larger, and corresponded more 
nearly in proportions with the anal. 
