„ , ACTINIARIA 

 204 



cycles, of which the first and part of the third are perfect. Two examined specimens show the following 

 arrangement of the mesenteries of the third cycle, counted from the one pair of directives i: imperfect, p: 

 perfect mesenteries. 



Sp. I (sectioned in transverse sections): pp — pi — pp — pp — ip — pp — ip — ip — ip — pi — ip — ip. 



The mesenteries, designated by spaced out figures, are weaker than the other perfect mesenteries, 

 and only reaching the actinopharynx with a small off-shoot. 



Sp. 2 (the largest specimen) only one half examined: ip — ii — ip — ii — ii — ii. As I have only 

 macroscopicaUy examined this specimen, it is possible that some of the imperfect mesenteries are in reality 

 perfect, but this I cannot with certainty decide as the specimen was rather badly preserved. On all accounts, 

 the size of the mesenteries of the third cycle shows that one mesentery of a pair has grown more rapidly 

 than its partner. A fully regular agroupment of these imperfect weaker and perfect stronger mesenteries does 

 not seem to be present. The weakest mesenteries of the third cycle are, however, as in Actinostola spetsbergensis, 

 commonly next to the mesenteries of the first order (compare P. densus). Both mesenteries of the pairs of 

 the fourth and the fifth cycles seem to be equally developed. The sterile and filament-lacking mesenteries 

 of the fifth cycle appear only in the proximal part of the body. 



The longitudinal muscles form no distinct pennons, though the outermost and innermost parts of 

 the mesenteries show a weaker muscularity than the intermediate parts. The folds of the muscles in the 

 best developed part are not especially strong, only the distal part shows high folds. The parietobasilar 

 muscles are distinctly marked, but hardly form any folds; they almost reach the sphincter. The basilar 

 muscles are distinct, though not strong, with few, rather high folds. Oral and marginal stomata are present 

 on the perfect mesenteries. The ciliated streaks of the filaments are well-developed. The mesenteries of the 

 third and fourth cycles have reproductive organs, the other mesenteries are sterile. The species is dioecious. 



Pycnanthus densus n. sp. 



Diagnosis: Pedal disc wide. Column thick, with indistinct, irregular longitudinal furrows. Sphincter 

 rather long, reticular, not stratified. Tentacles short, but broad, conical, tliick and irregularly, transversely 

 wrinkled in contracted state, about 90 to a little more than 100, and densely packed together, so that some 

 tentacles are sharply outlined from each other at the base. Outer tentacles not swollen at the base. Radial 

 muscles of the oral disc not distinctly interrupted at the insertion of the mesenteries, forming a net-work of 

 large meshes close to the ectoderm. Pairs of mesenteries about 92 to 108, in four primary, symmetrically 

 situated exocoels, more numerous than in the 2 other exocoels, which are situated on both sides of a directive 

 pair. Sometimes there is a difference in size of both mesenteries of the same pair of the third and fourth 

 cycles. Mesenteries of the last cycle only in the most proximal part of the body very small, without filaments 

 and reproductive organs. Parietobasilar muscles distinctly outlined, reaching to the large marginal stomata. 

 Typical nematocysts in the ectoderm of the tentacles numerous, 34 — 48 X 2,5 — 3 /i, in the actinopharynx 

 24 — 36 X 2 — 2,5(3,5) M- Spirocysts of the tentacles 22 X 1,5 — 2 to 58 X 3,5 (48 x 4, 5) fi. Nematocysts with 

 discernible basal part to the spiral thread in the actinopharynx 20 — 29 X 3 — 5 fi. 



Colour? 



