K^OETH AMEEICAX STAEFISHES. 



Ill 



Fig. 6.* 



OL't 



to the number of plates of the ambulacra! system. Genera where theie 

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



Fig. 8'. 



M"" C' fteV ■*■«■ 



(A I. 



Pig. 9. 



«lT 



ai/p 





at at v.-^ I 



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

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

 tacle ; a i, the interambulacral plates carrying papiUae p. The large terminal plate a'c at the actinostome 

 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 interambulacral 

 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 the body of the arm.. 

 The spur a' s of the terminal oral plate a'c sometimes forms a secondary cup-shaped plate along the 

 edge of the anus ; in Figs. 7, s a', and 8, a's, this plate is quite prominent, while in Fig. 6 it is less 

 developed. 



