I So MORRILL. [Vol. XI. 



In some cases the middle branch (2) of the third spinal nerve 

 does not divide before reaching the base of the second free 

 ray ; no branch is given in such a case to the third free ray. The 

 nerves supplying the first and second free rays divide in each 

 into two nearly equal rather large nerves and one or two small 

 ones near the base of the ray. The larger nerves lie in the 

 anterior and posterior portions of the rays and break up into 

 smaller branches in their course, which can be traced to the 

 papillated surface of the skin. There is considerable variation 

 in the branching of these nerves. 



Morphology of the Free Rays. 



The three free rays of the pectoral fins in both species of 

 Prionotus have the form of hooked finger-like appendages, the 

 distal third of each being bent almost at right angles to the 

 proximal two-thirds. When the fish is swimming the free 

 rays are held close to the body, and are hidden by the fins 

 viewed from above or at the side. The fish when resting 

 quietly on the bottom of a tank or pool brings these rays to a 

 position parallel to each other, with the somewhat knob-shaped 

 tips near the sides of the head, touching the surface on which 

 the fish is resting and along a line which makes an angle, pos- 

 teriorly, of about eighty degrees with the long axis of the body. 



These rays can be moved through an arc of 180°; a con- 

 siderably greater freedom of motion than is possessed by the 

 other rays of the pectoral fin. The free rays increase in size 

 from the first or anterior to the posterior, the latter being much 

 longer as well as larger than the first. In P. evolans, the free 

 rays resemble normal fin rays to a considerable extent. They 

 have, however, become imperfectly quadrilateral from the angle 

 outward, and arc slightly enlarged. In P. palmipes there 

 is considerable modification. Distally to the angle of the free 

 ray, it is pentagonal in cross section with a reentrant angle on 

 the faces which look backward when the ray is in the resting 

 position (Figs, i and 2). The anterior face is the narrower 

 and the outer the broader. The breadth of the distal portion 

 of the free ray increases from the angle for about one-third of 



