2 Hjalmar Théel, ■ 



sunk and settled on the bottom of the aquarium, the larva having passed 

 through all the metamorphoses in captivity. 



Besides, the following researches should fully remove the delusion, 

 met with in some zoological books, that the Echinocyamus is nothing 

 but the immature young of another Clypeastroid. Even Agassiz says 

 in his »Revision of the Echini»: »The development of the flat Oly- 

 peastroids and of the Scutellidfe as above described is most instruc- 

 tive, showing that we must introduce a complete reform among such 

 genera as Lenita, Scutellina, Runa, Echinocyamus, and other minute 

 Echinoids, which may eventually prove to be nothing but the young of 

 other Clypeastroids, probably of Mellita, Scutella, Laganum, Clypeaster, 

 Echinanthus, Encope, and the like». 



My studies on the embryology of Echinocyamus were carried out 

 at Christiueberg, the Swedish biological marine station, where I spent 

 the two summer vacations of 1890 and 1891, and I am greatly indebted 

 to its founder Professor SVEN LOVÉN for having kindly placed at my 

 disposal not only a working-table with aquaria etc., but also the residence 

 of the station. 



The following account is by no means complete, and consequently 

 it would have been desirable to put off its publication until I had had 

 the opportunity of renewing my visits to the west-coast of Sweden in 

 order to get the most obvious gaps filled up — but considering how un- 

 certain it is when this opportunity may occur, I prefer to publish it 

 now in its incomplete state. 



