133 



of the arms are perfectly smooth. The posterodorsal rods issue very near 

 the base of the anterolateral rods ; they are slightly widened at their base. 



Five specimens of this larva were found in a plankton sample from off 

 Taboga, the Gulf of Panama, taken in November 1915. 



Among some larvae presented to me many years ago by Prof .V. Hen sen, 

 Kiel, collected in January 1897 in the Bismarck Archipelago, there are a 

 few specimens of this same larval type. Unfortunately the skeleton has 

 been dissolved, and as the preservation is also otherwise poor, 1 shall give 

 no description of these larvse; but it is evident that we have here another 



Fig. 58. Skeleton of Ophiopluteus of Ophiocoma, species b. ^bo/^. Letters as in fig. 55. 



species of Op/iioco/ncr-larva, closely related to and very similar to species 

 a and b, but different from both, of course, since there is no species of 

 Ophiocoma common to these seas. 



Species c. (PI. XXX, Fig. 1). The shape of the body differs consider- 

 ably from that of species a and b, the hind end of the body being not nearly 

 so broad and flat as in those species; further the vibratile lobes are much 

 less developed. (In the figure the two ventral ones are directed outwards 

 and thus rather inconspicuous). The body is fairly elongated, the frontal 

 area large. The preoral ciUated band forms a high arch, and the postoral 

 band curves somewhat downwards in the middle, besides making a sUght 

 sinuation at each side. The arms are all short, the posterolateral ones only 

 slightly exceeding the body length, the other arms merely about half the 

 length of the body. They are all fairly broad and flat, but hardly widening 

 at the point. 



The skeleton (Fig. 59) is much more like that of Ophiocoma echinaia 

 than that of species a and b, the body rods being not horizontal, but rather 

 more erect than in 0. echinata. The posterolateral rods are sUghtly widened 

 a little beyond the" base (Fig. 60). The transverse rods are less widened 

 than in species b, and the end rods are directed straight downwards, while 

 in species b they are medially directed like the transverse rods. The rods 



