478 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



appear, and represent the terminal plates which, at an 

 early period, take up, and maintain throughout life, their 

 respective positions at the tips of the five arms. Fig. 27 

 represents a slightly more advanced stage. Here the 

 radial plates have enlarged considerably; and a sixth 

 plate, the central (en.), has appeared in their midst. The 

 five terminals have scarcely altered their respective posi- 

 tions ; and at a little distance anterior to them another 

 very minute tri-radiate plate (ad.) has appeared, and is 

 probably the madreporic plate. Further than growth of 

 the several plates, little change is represented in fig. 28, 

 though three of the terminals have become slightly more 

 complex. In fig. 29, however, the future Ophiurid is seen 

 to be taking shape. The central and the five radials have 

 increased considerably in size and still lie to the right of 

 the larva. The terminals are seen to be taking up their 

 respective positions; and a few very minute plates, pro- 

 bably adambulacrals, have appeared. In the specimen 

 from which fig. 30 was drawn the plates of the 

 apical system — central and radials — have taken up their 

 permanent positions, with the terminals in exact correla- 

 tion with the radials. In fig. 31, PL IV, the aboral 

 skeletal plates of the still pelagic post-larva are repre- 

 sented. In the living post-larva of this age a pair of 

 tube-feet in each ray may be seen in active movement, 

 and are functional as organs of locomotion. 



Abundant in July, 1907 and 1908, " ophio- 

 pluteus mancus ' ' was represented only sparingly 

 in 1909, since when its occurrence has been rare. 

 Graham Kerr (6) records the common occurrence of 

 this species in September in Loch Sween. He 

 distinguishes it by the letter C, and appears to have 

 some doubt as to its identity with Mortensen's ophioplu- 

 teus mancus. There is, however, no doubt that his, 



