92 THE VOYAGE OF H.M.S. CHALLENGER. 



Family, Ilyanthid^, Gosse, pro parte. 



Hexactinise, having the aboral end of the Ijody rounded ; without pedal disk. 



As I include in the family of the Ilyanthidse only those forms which have the septal 

 arrangement of the Hexactinise, I define it in a much more limited sense than Gosse 

 (Actinologia Britannica, p. 227) or even Verrill (Memoirs Boston Soc, vol. i. p. 26). 

 Verrill has detached the Cerianthidse only, but left the Edwardsise in the family, while 

 AUmann (Quart. Jour. Micr. Sci., new ser., vol. xii. p. 394), my brother and myself 

 (Actiuien, p. 124), and Angelo Andres (Mittheilungen der Zool. Stat, zu Neapel, Bd. ii. 

 p. 123) have most clearly pointed out that the latter also ought to be separated. I 

 am of the opinion that even excluding the Edwardsise does not free the family from 

 foreign elements, for it is not at all likely that Halcampa alhida and Halcampa producta 

 with twenty tentacles, Halcampa microps with sixteen tentacles, &c., conform to the 

 hexamerous type of arrangement of the tentacles. 



By the absence of the pedal disk the Ilyanthidse form a transition to the tribe 

 Edwardsise, on account of which I have placed them at the end of the Hexactiniae ; 

 in tlicir internal anatomy they are also allied to the Edwardsise. Halcamjm clavus, 

 especially, which I am now about to describe, is so clearly an intermediate form that I was 

 for long dubious whether I should treat of it under the Edwardsise or the Hexactinise. 



Halcampa, Gosse. 



Ilyanthidse with elongated, vermiform body ; without sharply defined circular muscle ; 

 the posterior end may be distended into a vesicle ; oesophageal grooves indistinct or 

 wanting. 



In all systematic descriptions of the Ilyanthidse published by former authors, the 

 genera Edwardsia and Halcampa are placed very close together ; according to Gosse, 

 they are only distinguished from one another by the facts, that the middle part of the 

 body in Edwardsia is surrounded by a sheath, an " epidermis," which is wanting in 

 Halcampa, and that the body is divided into three sections, the " capitulum," the 

 "scapus," and the "physa." Angelo Andres {I. c, p. 137) has recently made use of a 

 much more important anatomical character, viz., the presence of only eight septa 

 (" octoseptazione ") in Edwardsia, while there are always at least twelve septa in 

 Halcampa. I only attach importance to the different arrangement of the septa, and 

 therefore will place forms with tripartite wall in the genus Hcdcampa, provided only 

 that they be true Hexactinise. 



Halcampa clavus (PI. III. figs. 1, 4, 10 ; PI. XII. figs. 8, 9, 11 ; PL XIII. figs. 2, 

 4-7). 



Actinia clavus, Quoy et Gayraard, Voyage de 1' Astrolabe, Zoologie, iv. p. 150, pi. x. figs. 6-11, 1833. 

 Iluanthus clavus, Milne-Edwards, Histoire des Corall., torn. i. p. 284. 



