On Arachnactis brachiolata. 529 



mont of the tentacles appears to be the same. There are 

 at first four tentacles of which two arc much larger than 

 the others, and between the largest ones is formed the odd 

 tentacle, which Haime considered as a tentacle of the sec- 

 ond cycle, but which I have shown to remain always odd 

 in Arachnactis. When we compare the figures given by 

 Busch * of Diantheus nobilis, which is undoubtedly, as 

 Leuckart f thinks the young of Cerianthus membranaceus, 

 or of Saccanthus, we shall find still greater resemblances 

 to the figures I have given of our Arachnactis. As the 

 stages observed by Busch are more advanced than those 

 of Haime, there can be no doubt after examining his fig- 

 ures that the mode of development of the tentacles of 

 Cerianthus is identical with that of Arachnactis. We have 

 then in the family of Cerianthidae as established by Milne 

 Edwards, $ (he does not include in it Arachnactis,) a mode 

 of development of tentacles which is entirely difl'erent 

 from what we find in the other actinias. This mode of 

 development is f&und in genera which are connected by 

 structural differences, which would seem to prove that here 

 we have a group of greater value than a simple family, 

 which must rank as a suborder in the order of Actinaria, 

 and include in it two families of which Cerianthus and 

 Arachnactis are the representatives. 



In these actinise the partitions of the same cycle are of 

 different lengths, two of them always retaining their greater 

 predominance. They have two sets of rows of tentacles, 

 one round the mouth, the other round the edge of the disk, 

 plainly showing that Cerianthus and Arachnactis form a 



* Busch, \V. Beobachtungen iiber Anatomie uud Entwickelung einiger wir- 

 bellosen Seethiere. Berlin, 1851. 



t Leuckart, R. Bericht iiber die Leistungen in der Naturgeschichtc der nie- 

 derea Thiere wiihrend der Jahre 1848-1853. Arcbiv fiir Naturgeschichte, 1852, 

 ii. p 461. 



X Edwards, H. Milne. Histoire Naturelle des Corallaires, Tome i. Paris, 

 1857. 



JOURNAL B. S. N. H. 67 



