138 



rod could not be made out; but in any case it is somewhat curved and 



distinctly longer than in species a. 



One specimen from the Malacca Strait, 7° 20' N. 98° 4' E. 7/IV, 1900. 

 Another specimen from the Malacca Strait (5° 53' N. 95° 43' E. 28/XI, 



1899) is intermediate in its characters between the two above species. The 



ventral median process is as long as the dorsal, but very slightly spinous. 



The posterolateral rods are strongly thorny as in species b, but the canal 



cannot be discerned. The preoral rod ap- 

 pears to be as in species a, but as it lies 

 in a different position in the preparation, 

 direct comparison with that of the two 

 other species is impossible; on the other 

 hand it affords an excellent view of this 

 rod in side view (Fig. 65). The accessory 

 rod appears to be lacking. The length of 

 the arms is about as in species a. In this 

 specimen, as well as in the type of species 

 b, the primary lobes of the hydrocoel have 

 not yet been formed. 



On account of the insufficiency of the 

 material available it is impossible at pre- 

 sent to decide whether this latter specimen 



belongs to species a or, perhaps, represents a third species. That, at least, 



the two forms described as species a and b are distinct species seems, 



however, beyond doubt. 



It is quite impossible to give any reasonable suggestion as to which 



Ophiurid may be the adult form to which this very interesting larval type 



belongs. 



Fig. 65. Side view of preoral rod 

 of Ophiopluteus costatus. "'"/i- 

 dm. dorsal median process. 



Ophiopluteus undulatus nova forma. 



This larval form is especially characterized by its peculiar, undulated 

 posterolateral rods. The body skeleton is of the compound type, very short 

 and compact; the transverse rods are simple, without processes. The rods 

 of the arms are very smooth; only on the posterolateral rods there may 

 be an indication of thorns. 



On account of the character of the body skeleton the posterior end of 

 the body is rounded, the end rods forming only a very slight prominence 

 or none at all. The frontal area apparently as a rule low, but wide. The 

 stomach is very wide, the esophagus short. There appears to be a slight 

 widening in the point of all the arms. Pigmentation unknown. 



