137 



lateral arms being somewhat shorter than the postoral and poslerodorsal 

 arms. 



Skeleton (Fig. 63). The body skeleton is somewhat more robust than in 

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



Fig. 63. Skeleton of Ophioplule.ns costatii*. species b. 

 Letters as in fii^. 61. 



Fig. 64. 



Part of 



postero- 



lateral rotl 



of Ophiopl. 



costatus, 



species b. 



400 /i 



of the anal lobe; it has some conspicuous side branches, while 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 "canal" 

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

 64), 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 



