137 



lateral arms being somewhat shorter than the posloral and posterodorsal 

 arms. 



Skeleton (Fig. 03). The body skeleton is somewhat more robust than in 

 species a. The ventral median process is long, reaching lo the anterior edge 



Fig. 63. .Skeleton of Opiiiopluleus coslaliis. species b. 

 Letters as in fig. 61. 



Fig. 64. 



Part of 



postero- 

 lateral rod 

 of OphiopL 



coslatus, 

 species b. 



of the anal lobe; it has some conspicuous side branches, wliik" the dorsal 

 median process, which is of about the same length, is simple, pointed, only 

 with a few backwards directed thorns in the lower part. The posterolateral 

 rods are set with much larger thorns than in species a. and the "canar" 

 is quite short, reaching only from the lowermost to the third spine (Fig. 

 ()1), and there is no widening at its upper end. The preoral rod reaches 

 much farther down on the ventral side, beyond the preoral and even over 

 the postoral band, so that a flap of the frontal area proceeds downwards 

 over the oral area, covering the mouth. The exact shape of the accessory 



18 



