\4?. Records of ihc Indian Museum. [VoT,. XA'', 



branclis. As is well kno's\Ti, the external form of the tail fin of Torpedo 

 is symmetrical ; internally, however, the ventral fin-rays are directly 

 borne by hypurals, the two terminal ones being strongly developed, 

 fused at their bases both to one another and to the last centrum. Above 

 the last hypural are to be seen the remains of the neural arches of vanished 

 centra, occasioned by the abbreviation of the vertebral column ; they are 

 still to be found because they are necessary to provide protection for the 

 terminal portion of the spinal cord. All the ventral supports are hy- 

 purals, while dorsally the rays are borne exclusively by radials which 

 have not fused with the neural arches. 



It is possible that an investigation into the tail fin of the Rays may 

 prove to be of considerable value ; while Torpedo thus possesses what 

 may be regarded as a fairly specialized type of horaocercy, others may 

 shew a simpler tendency in that direction. 



