1881.] PROF. F. J. BELL ON THE ECHINOMETRIDiE. 



Strongylocentrotus PURPURATUS. 



429 



Strongylocentrotus tuberculatus. 



Owing to the fact that the number of species in this genus is, 

 among the Echinoidea, so large, I have added to the Tables just given 

 others, which show certain points in the characters of the diiferent 

 species which are undoubtedly of specific value. 



I have for these points examined every species which is repre- 

 sented in the national collection ; and I have to express my hope 

 that other observers will fill in the lacunae in our knowledge of the 

 points now to be discussed. 



Relations of the Ocular Plates to the Anal Area. 



(u) All shut out i. bullatus. 



ii. lividus 



(and, as we may snppose, ffaimardi). 

 iii. depressus. 



(ft) Two touch iv. armiger. 



v. drobachiensis. 

 vi. erythrogrammus. 

 vii. franciscanus. 

 viii. inlermedius. 

 ix. purpuratus. 

 X. tuberculatus, 



(y) Three touch xi. gibhosus. 



(?) Four touch xii. albus^. 



' This is true of full-grown specimens. In the younger all the oculars may be 

 shut, off; but it is possible that four of these have even tlieu a diflerent position 

 to the fifth, or one lyiug to the right of the madreporic plate. 



