1 15 



of one species, of 

 the same eminently 

 characteristic lar- 

 val type, occurring 

 together in the 

 same locality and 

 at the same time 

 of the year. 



It is useless to 

 meditate over the 

 problem to which 

 genus of Ophiurids 

 these larvae belong. 

 The fact that it is 

 known only from 

 the Gulf of Panama 

 is not a sufficient 

 indication for solv- 

 ing the problem. 



Fig. 71. Skeleton of Ophiopluteus fulcitus, species c. 29 %. 

 s. supporting rod. 



Ophiopluteus opulentus nova forma. 



A very marked feature distinguishing this larval form from all the 

 Ophiurid larvae hitherto known is the presence of a pair of short extra 

 arms on both the ventral and dorsal sides, proceeding from the lower part 

 of the postoral and the anterolateral rods, below the point where the 

 posterodorsal rod issues from the latter. These extra arms are very much 

 shorter than the other arms and, upon the whole, hardly of the same 

 morphological value as these; but their structure is the same, the ciliated 

 band passing out along them in the same way as in the usual arms. 



The body skeleton is of the compound type. There is a pair of small 

 processes from the middle of each transverse rod. The posterolateral rods 

 are canaliculate to a greater or lesser extent. The end rods are of medium 

 length, straight, trifid at the point. The posterolateral arms are about 2 3 

 times as long as the inner arms. 



Species a (PI. XXI, Fig. 3). The posterolateral arms about twice tin- 

 length of the inner pairs of arms, which are thin and round, ending in a 

 small widening. It is uncertain whether there is any widening at the point 

 of the posterolateral arms. The body is fairly large, the inner arms measur- 

 ing about ! J /2 the length of the body. The frontal area is distinct, but 

 not large. 



19 



