ECHINODERM LARVAE. 481 



numbers " in the waters of Loch Sween, in the early part 

 of August, 1911. ' Also, he precedes Gravely and myself 

 in recognising its resemblance to Mortensen's ophio- 

 pluteus henseni, as figured in his " Echinoderm Larvae 

 of the Plankton Expedition," and we agree with him in 

 regarding the two as distinct. 



The ophiopluteus represented in figs. 39 to 42, PI. VI, 

 is almost certainly the pluteus paradoxus of Miiller, 

 which is correlated by Mortensen (12) with Ophioglypha 

 alb i da (Forbes), now more correctly known as 

 Ophiura albida. It is easily distinguished by its broad 

 arms, the postero-lateral ones rather strongly curved, 

 and by the cap of ciliated cells — possibly a sense organ — 

 which covers the posterior end of the body, and is always 

 rendered conspicuous by staining. The only particular in 

 which this Port Erin form differs from that figured by 

 Mortensen is the absence of the sharp, well-developed 

 spines which are represented as projecting at right angles 

 from the skeletal rods of the arms. Graham Kerr (6) 

 found an ophiopluteus in Loch Sween which he considers 

 identical with that figured by Mortensen; but in his 

 figure as in mine the skeletal rods are represented as 

 spineless. Fig. 40 represents an early stage in the meta- 

 morphosis of this larva. The hydrocoel has almost com- 

 pletely surrounded the oesophagus. On the left side of 

 the body and overlying the large, oval stomach, are five 

 rounded elevations, each supported by a crescentic 

 terminal plate (tl.). These are the rudiments of the five 

 arms of the adult Ophiuroid ; three being situated dorsally 

 and two — indicated by terminals figured in black — ven- 

 trally. On the right side the central (en.) and the five 

 radials (rl.) are seen. On the left side, anterior to the 

 terminals and overlying the hydrocoel, is a small adani- 

 bulacral plate (ad.), and on the extreme right is the 



