808 Proceedings of the Eoyal Irish Academy. 



James Clark ; but lie suggests that it is improbable tliat the 

 same species should oecui' on both sides of the Atlantic, and 

 refers all the European members of the genus to the foimer 

 species, and retains the name auricula for the American fonn 

 only. Although, strictly, that name being older than octoradiatus 

 should be used for the (on his riew) siagle European species. 



From this view I strongly dissent. In the course of exami- 

 nation of Teiy many Hcdiclystus from Valencia, Falmouth, and 

 Plymouth, 1 as well as single specimens from Jersey and the 

 Isle of Man, I have entirely failed to meet -vrith a single adult 

 specimen agi'eeing with the descriptions of H. octoradiatus. I 

 have seen only few large specimens, but all are in my opinion 

 S. auricula. The rest may be arranged according to size in a 

 series, exhibiting the stages of growth and evolution of 

 character. There appears to me no reason for doubting that 

 they are one and all members of the same species having 

 characters appropriate to their size. 



The distinguishing features of the two species are these 

 (taken chiefly fi'om Haeckel, who gives concise diagnoses) : — 



S. octoradiatus — Arms arranged at equal distances apart, the 

 perradial and interradial bays of the sub-umbrellar margin being 

 equal ; marginal anchors (colleto-cystophores) egg-shaped or 

 almost club-shaped, smaller than in S. auricula ; each arm with 

 30-60 tentacles; genital bands aiTanged at equal distances 

 apart, each band composed of 20-30 large sub-equal saccules 

 arranged in two longitudinal rows. 



S. auricula. — Arms approximated in pairs, the perradial bays 

 of the sub-umbrellar margin twice as wide and deep as the 

 interradial ; mai'ginal anchors coffee-bean shaped, large ; each 

 arm bearing 100-120 tentacles; genital bands approximated in 

 pairs, broadly triangular in shape, each band consisting of about 

 125 saccules aiTanged in 6-8 longitudinal rows, the size of the 

 saccules increasing from the interradial border across the band 

 to a maximum on the perradial border. 



Haeckel also speaks of some difference in the shape and pro- 

 portions of the umbrella ; a matter of little practical value in 

 the case of animals so apt to change their* shape every few 



* It has been customary at the Plymouth Laboratory to label the local form, 

 H. octoradiatus. I am not aware by whom, and npon what grounds, the determi- 

 TiiUion was originallv made. 



