151 



Ophiopluteus formosus nova forma. 



Body skeleton compound; no processes from the transverse rods. The 

 posterodorsal rod issues near the base of the anterolateral rod; postero- 

 lateral rods simple, with numerous, fairly large, curved thorns along the 

 inner side; the other rods smooth. 



This larval type is not distinguished by any specially marked characters, 

 the low point of issue of the posterodorsal rods being the most conspicuous 

 feature. The larva is a very typical, regular form, of a beautiful, graceful 

 shape. 



Species a. (PI. XXVII, Fig. 1; PI. XXX, Fig. 2). The body is fairly 

 large; the inner arms hardly as long as the body, the posterolateral ones 



Fig. 79. Skeleton of Ophiopluteus formosus, species a. "'"/i- Letters as in fig. 61. 



about twice that length, gracefully bent. The preoral band is straight in the 

 middle, turning rather sharply downwards at the sides; the postoral band 

 with a slight sinuation at each side. At the base of the posterolateral arms 

 the band makes a deep downward curve, forming an incipient vibratile 

 lobe. The frontal area is not very large. Arms fairly broad and flat. 



In the skeleton (Fig. 79) the somewhat widened, lobate ends of the trans- 

 verse rods are noticeable; otherwise there are no very prominent features. 



5 specimens from the Gulf of Panama, near the island of Taboga, in 

 December 1915. 



One specimen is in the metamorphosis stage (PI. XXX, Fig. 2) the inner 

 arms, except the right postoral one, having been absorbed; also the left 

 posterolateral arm has begun to undergo absorption. The outstanding fea- 

 ture of this stage is the arrangement of the vibratile bands. The two bands 



