162 



urid proceeds in the same way as in 0. bimaciilalus and 0. senatus (see 

 under the latter species). Neither are any of the specimens of the species 

 a and b in the metamorphosis stage. In any case it shouUi be kept in 

 mind for future investigation, that these larvae possibly have some nearer 

 affinity to one another. 



At our present stage of knowledge it is impossible to form an opinion 

 of any value as to which forms of Ophiurids the larval type of ()j)hi<)- 

 pluteus arcifer belongs. The existence of species of this larval type in the 

 East Indian Seas, in the Gulf of Panama and in the West Indies is, of 



y 



< 



^ 



r 



^ =lr 



Fig. 88. Skeleton of Ophiopluteus arci/er, species c. ^""Z,. A. Part of posterolateral roil; 

 B. the same rod, probably showing regeneration. C. body skeleton, seen slightly from above. 



course, a fact of importance, but not in itself sufiicient foundation for 

 a reasonable suggestion as to the solution of this problem. 



Ophiopluteus monacanthus nova forma. 



PI. XXX, Figs. 3—4. 



From off Jolo (21/III. 1914) there are two specimens of a very peculiar 

 Ophiurid larva, which seems to me well worth describing, although the 

 fact that the skeleton has been dissolved prevents giving a complete 

 description of it. The outstanding feature of this species is the presence 

 of a very strong median process on the ventral side alone: it projects at 

 a right angle to the body, forming a large hump on the ventral side, while 

 the dorsal side of the body remains flat, there being evidently no median 

 process from the dorsal transver.se rods. There is a widening on the rectum, 

 filling out the hump. In its general appearance the larva otiierwise recalls 

 Ophiopluteus arcifer. The postoral band makes a small, but very distinct 

 backwards curve at each side. The posterolateral arms are somewhat more 



