968 PROF. J. p. McMURRicn ox 



of the I'est of the stoiuatodjeum and forms a well-marked deep 

 groove, whose endoderm is much higher than that of the rest 

 of the stomatodseum, although it does not present a reticular 

 formation such as occurs in Peachia qibhiquecapitata. There are 

 six pairs of mesenteries, all of which are perfect and all possess 

 mesenterial filaments ; no indications of additional mesenteries 

 of the second cycle were to be found. Two of the six pairs 

 were directives. The longitudinal musculature (iig. 7) formed 

 a low pennon extending throughout the entire muscular area 

 of the mesentery, the supporting lamellte being palisade-like 

 in their arrangement, and is higher than the endoderm that 

 covered them. No parieto-basilar muscle was present in my 

 preparations, which did not, however, include the most proximal 

 portion of the column. 



A number of immature Actinians, a list of which has been 

 given by Haddon (1887), have been described as pai^asites in 

 various species of Medusfe, and all present structural features 

 sufficiently similar to suggest that they are generically identical 

 with one another and with the form described above. They have 

 been assigned in part to the genus Halcampa and in part to 

 Peachia, but none of these has yet been actually shown to trans- 

 form into the one or the other of these genera., and until the 

 adult condition is definitely known it seems well to retain 

 for them the genus Bicidium established by L. Agassiz (1859), 

 recognizing, however, that this is but provisional and that the 

 forms assigned to it are larval or at least immature. 



The evidence furnished by the structure, although not con- 

 clusive, does however give some indications of the probable 

 position of the adult form and, I believe, points towards the 

 genus Peachia, rather than to Halcampa. Difierences between 

 the two genera that are pertinent to this question are to be found 

 in the presence of a conchula in Peachia and its absence in 

 Halcampa ; in the single deep siphonoglyph of Peachia as 

 compared with the two shallow ones of Halcampa ; and in the 

 somewhat diffuse form of the muscle pennons in Peachia as 

 compared with the compact and circumscribed ones of Halcampa. 

 The first of these differences is not apparent in all species of 

 Bicidium, the conchula probably being late in its development, 

 but the other characteristics are constant in all known forms 

 whose anatomy has been recorded. 



Since Haddon (1887) I'eviewed the various species of Bicidiuin 

 some additions have been made to our knowledge of them, and in 

 support of my contention as to their affinities to Peachia rather 

 than to Halcampa, a reconsideration of them may not be amiss. 

 The absence of a conchula in B. cequoreai is, it is true, opposed to 

 its reference to Peachia, but, as has been pointed out, this 

 structure may very well be late in developing, and in the nature 

 of the siphonoglyph and the muscle pennons the similarity to 

 that form and the difference from Halcampa are pronounced. 



