ZOANTHARIA 59 



the nematocysts with twisted thread are very scarce. The mesoglaa is generally thick, so that the 

 difference in thickness between this and the mesoglcea of the siphonoglyphe, which is somewhat 

 thickened, is not so great as is usual among the Zoanthidae. The entoderm is thin and several times 

 thinner than the ectoderm. 



I have examined the arrangement of the mesenteries in 3 specimens, namely, 2 of those 

 represented in fig. 19, PI. I, and 1 from the Michael Sars Expedition. The first had 36 mesenteries, 

 19 on the one side, 17 on the other, otherwise the arrangement was typical according to the macro- 

 type, the two mesenteries lying nearest the sulcus, one on each side, being micro-mesenteries. The 

 second specimen had 38 mesenteries, 18 on the one side, 20 on the other, the third 36 mesenteries, 

 18 on each side; in the last two cases the mesenteries lying nearest the sulcus were rnaeromesenteries. 

 As the oesophagus in the aboral part is very wide, the mesenteries there become short, so that in the 

 glandular tract and genital region they only occupy a small part of the gastrovascular cavity; the 

 micromesenteries are moderately developed. The longitudinal muscles were strong but no folds 

 were seen on my specimens; the parieto-basilar muscles were neither broad nor furrowed, they reach a 

 long way on to the body-wall. 



The filaments are very large and strong. The mesoglcea in the glandular region is very thick 

 both in the intermediate tract and the glandular tract. This is undoubtedly in connection with the 

 fact, that the mesoglcea of the oesophagus is so thick. The filaments thereby assume a very robust 

 appearance. The ectoderm of the intermediate and the glandular tracts contains numerous thick-walled 

 nematocysts, the spiral thread of which is plainly visible. They are much longer than in the 

 oesophagus (length ca. 26— 29/j, in the North American form they are in greater agreement with the 

 capsules in the oesophagus, breadth ca. 5 p). Further, I have even observed some few large capsules 

 of the same appearance as those in the body-wall but larger (length about 31^, breadth half the length). 

 Both the North American specimens sectioned by me were sexually mature and in both cases 

 also ovaries were present. 



Systematic remarks. As indicated by me in the synomymy list, the variety of C.americanus 

 figured by Verrill in the Report on the Blake Expedition was no other than Norman's Parazoanthus 

 anguicomus. 



The three species P. haddoni, dixoni and anguicomus are evidently so closely related to each 

 other, that in many cases it seems difficult to separate them, and especially P. haddoni and dixoni are 

 very much alike in outer appearance. As Prof. H add on, who had at his disposal a larger material 

 of P. haddoni and P. dixoni than I have had for investigation and who also several years ago was so 

 kind as to examine a colony (a coloured one with large polyps) of P. haddoni sent him by me, is of 

 opinion, however, that they differ, I think I ought to consider them as two different species, though 

 it is difficult to find really good distinguishing characteristics, especially in material which is not well 

 preserved. The nematocysts agree quite well in haddoni and anguicomus, whereas they are some- 

 what but not very much larger in P. dixoni. In a colony of P. dixoni sent me by Prof. Haddon 

 I found the following series of capsules. The large nematocysts of the body-wall with greatly twisted 

 thread were 46—53^ long and 19—20^ broad, the smaller ones found in the capitular region were 

 26—29 f* l° n & an d 13— 15 (i broad and occurred in quantities. The thick-walled capsules in the 



