1898-1902. No. 13.] 



ECHINODERMATA. 



The proportion of the disc-radius to the arm-radius varies between 

 1 : 1.74 and 1 : 2.50. As the table shows, however, most of the speci- 

 mens belong to the long-rayed form, with an arm-radius more than 

 twice the length of the disc-radius. 



There are from 3 to 8 inner ambulacral papillae (PI. 1, fig. 2), most 

 frequently 4 or 5. On the adambulacral plate nearest to the oral plate, 

 there may be as many as 8. In old specimens, the number of outer 

 ambulacral papiliffi, transverse papillae, is generally 6, but varies between 

 3 and 7; while on the plate nearest to the oral plate, there are some- 

 times only 2 papillse. In young specimens there are never more 

 than 5. 



