8 



Mindeskrift for J. Steenstrup. X. 



would seem to show that O. tigris is not identical with O. elegans ; but, as Lyman 

 justly points out, the ventral piates ( — which he has evidentJy seen quite correctly — ) 

 vary considerably in shape in the same specimen, so that it is doubtful whether 

 this difference is so constant as to warrant the separation of the two forms into 

 two species. 



The alleged absence of the ventral piates in Ophioteresis has here- 

 with been proved to rest on insufficient examination. The piates occur 

 in this species as in other Ophiuroids, but are obscured by a thick skin. Hence 

 the open ambulacral furrow is reduced to a myth. As a matter of faet the ambulacral 

 furrow lies rather deeper than usual in the arm, as can be seen in Bell's figure 

 represented in textfigure 1. 



As to the dorsal piates they are stated by Lyman to be „represented by 

 a double row of irregular elongated warts, which just at the base of the arm are 

 increased in number so as to form a clump of different-sized pieces," and Bell also 

 says that they are „definitely double". It is a curious faet that while the ventral 

 piates, which are said to be wanting, are really present, the dorsal piates, which are 

 said to be double, are really wanting. In faet, the two elongated lateral warts 

 seen on the dorsal side of each joint (PI. I Fig. 8) are really parts of the vertebra. 

 (Comp. the figure of the dorsal side of the isolated vertebra, PI. II Fig 4;. On treat- 

 ing the arm with Eau de Javelle no piates can be detached from the dorsal side. 

 The lines represented in Bell's figure (textfigure 1) as separating the ,, dorsal piates" 

 from the vertebra do not exist. However, traces of dorsal piates may be observed 



at the point of the arms (PI. I Fig. 1) ; in 

 this figure is shown near the middle line at 

 the base of the third joint a small, three-ar- 

 med plate, which may perhaps represent a 

 dorsal plate. On the following joints there 

 is a small plate on each side (also on the 

 third joint the rudiment of such a plate is 

 found on each side). These lateral piates are 

 evidently absorbed in the course of growth ; 

 I have been unable to ascertain from about 

 which joint they have disappeared. It can only be said that they are not found on 

 the fullgrown joints. In the four-armed specimen I find on one arm a small median 

 dorsal plate on the two outer joints, but no lateral piates, while on the following 

 joints neither median nor lateral dorsal piates are to be observed. As Lyman 

 correctly describes, there are at the basis of the arm in O. tigris several dorsal piates 

 of different sizes and the same appears to be the case in O. elegans, judging from the 



Fig. 1. Armjoint of Ophioteresis, seen from 



the aboralside. (Af ter Bell, from Gregory). 



a. articular cavities. d. dorsal piates. 



1. lateral piates. 



