IsOETH AMEEICAN STAKFISHES. 



Ill 



CLt 



/> > 



to the number of plates of the ambulacral system. Genera where there 

 are large marginal plates, as in Astropecten, and the pentagonal Star- 



Fig. 8', 



Fig. 9. 



at dc L-/ ( 



* In Figs. 6, 7, 8, c' r are the small plates or spurs forming the ridfije covering the ambulacral groove ; 

 a' c, the corresponding plates of the ambulacral plates a'; ao, the opening for passage of ambulacral ten- 

 tacle; ai, the interambulacral plates carrying papilla; p. The large terminal plate a'c at the aciinostome 

 encroaches upon the corresponding ambulacral plate, so as to cover it by a spur a' s, so much so that, 

 when seen from above, this plate appears to be directly connected with the terminal interambu'acral 

 plate a ip, but the profile view clearly shows in all these genera that the terminal plates, although of 

 different proportions, do not differ in their arrangement from those forming tlie botly of the ;irm. 

 The spur a' s of the terminal oral plate a'c sometimes forms a secondary cujvshaped plate along the 

 edge of the arms; in Figs. 7, s a', and 8, a' s, this plate is quite pix/uiiucnt; while in Fig. 6 it is less 

 developed. 



