159 



They cause a very prominent elevation of the body-wall, like a hump, on 

 both the ventral and the dorsal side of the body. 



The body is comparatively low, with a low frontal area. The preoral 

 band is generally almost straight. A noteworthy feature is the more or 

 less conical shape of the esophagus (especially so in species a). The arms 



Fig. 85. Body skeleton of Ophiopluteus areifer, species a. A. in side view, ^'"/i; B. oblique 

 dorsal view. al. anterolateral rod; b. body rod; dm. dorsal median process; e. end rod; 

 pd. posterodorsal ; pi. posterolateral; po. postoral rod; r. recurrent rod; tr. transverse rod; 



vm. ventral median process. 



are slightly widened at the point. The posterolateral arms are 3 — 5 times 

 the body length, rather obliquely outwards directed. The other arms are 

 not much more than body length, their point being at about a level with 

 the point of the posterolateral arms. The body skeleton is of the com- 

 pound type. 



Species a. (PL XXVI, Fig. 1). The posterolateral rods are set with 

 bilaterally arranged small thorns, which give the rod a peculiar, almost 



