135 
no premises. But that I did not do. Herewith I do not mean to 
try to justify all the references of Echinoderm larvæ which I have 
ventured to suggest. The premises may have been wrong in some 
cases, and then, of course, the conclusions must also be wrong, e.g. 
in the case of the larva supposed to belong to Echinometra lu- 
cunter, * 1 ) — a very singular case which I am as yet unable to explain, 
the more so as new facts gathered seem to indicate the correct- 
ness of the premises that led me to the said conclusion, which I 
have myself proved to be wrong. 2 * ) In this case something must, 
of course, be wrong in the premises; what it is, remains to be 
disclosed. 
I. Ophiura affinis Ltk. (?). 
One of the first days of August this year I found in the plank¬ 
ton an Ophiuroid-larva, which recalls most strikingly that figured 
by Joh. Muller in his VI. memoir on Echinoderm larvæ, 8 ) Taf. 
VII, figs. 5—6, which larva was observed by him in the Adriatic 
Sea in the summer 4 * ) of 1852. So far as I know this larva has 
not been observed again till now. 
In the general features there is perfect accordance between 
Miiller’s larva from the Adriatic and the one observed by me at 
Kristineberg, and also the skeletal structure appears to be quite the 
same (—unfortunately I have only a drawing, but no preserved spec- 
imens of the larva, which was seen only one day, and I could not 
there compare it with M ii 11 e r’s figure of the larva, M ii 11 e r’s work 
being not available at the station —); especially the very character- 
istic sinuation at the point, where the body rod and postero-lateral 
rod join, mentioned by Muller, was well marked in the specimens 
observed by me. Only the coloration was not quite the same. 
*) T,h. Mortensen. Uber die Larve von Echinometra lucunter (L.) (?). 
Zool. Jahrbiicher. Suppl. XV. 1912. 
l ) Th. Mortensen. On the Development of some West Indian Echin- 
oderms. Year Book No. 15 of the Carnegie Institution. Washington, 
p. 193. 1916. 
*) Uber den allgemeinen Plan in der Entwickelung der Echinodermen- 
Abhandl. d. Berliner Akad. 1852. (1853). 
4 ) The exact time, when it was observed, is not stated by Muller, but it 
appears to have been in the summer time. 
