12 DR. Til. MORTENSEN. 



long, straight, trifid at the point. The postero-lateral rods are provided 

 with thorns along the inner side, and also the antero-lateral rods are 

 slightly thorny. (These thorns will doubtless be considerably more 

 numerous in the fully developed larva . ) It must be pointed out that there 

 is no posterior tuft of cilia ; the frontal area is quite small. Other- 

 wise there is nothing to be remarked concerning the shape of the larva,. 



Fig. 13. 



Fia. 13. — Skeleton of tlie Ophiopluteus of Ophiadis Balli. cr, cross-rod ; e, end-rod; 

 r, recurrent rod. 275/1. 



in this stage at least ; it has the typical Ophiofluteus shape, as appears-- 

 from the shape of the skeleton. 



It is very satisfactory that the larva of this species could be reared to- 

 a sufficiently advanced stage for recognition, this being the first informa- 

 tion of the larval form of a species of the genus Ophiactis. (The two 

 species Ophiactis Kroyeri (L.) and 0. asperula (Phil.) appear to be vivi- 

 parous.*) 



IV. — Ophiocoma nigra. 



It was not until towards the end of June that this species was found to 

 contain ripe sexual products. On the 25th June some specimens were 

 put in a jar in the same way as Ophiactis, and the next day some fertil- 

 ized eggs were found. It was no large number, and I then repeated the 

 experiment, but without success, evidently because the specimens were 



* H. Ludwig, " Brutpflege bei Echinodermen." Zool. Jahrhiicher, Suppl. YII, 1904,. 

 p. 693. 



