10n Canadian Arctic Expedition, 1913-18 



are of the simple, wavy, leaf-like form characterizing that genus, extending 

 practically the whole length of the radial canals. 



The arrangement and structure of the marginal organs in Eperetmus is 

 characteristic. And in spite of the poor condition of the present material, 

 enough tentacles and otocysts are still intact to show the same main features. 

 Thus the tentacles are all of one kind, corresponding to the primary tentacles 

 of Olindias, neither the marginal papillae characteristic of Gonionemus, nor the 

 secondary (velar) tentacles of Olindias occurring. Tentacles are present in all 

 stages of growth, from mere knobs to the fully developed state. And while the 

 youngest stand free on the margin, with progressive development they turn 

 upward against the exumbrella, and finally come to lie in deep furrows in the 

 latter, from which they project at various heights, corresponding to their ages. 

 One of the most diagnostic features is the presence of a thick opaque kidney- 

 shaped nematocyst pad associated with each large tentacle, lining the distal 

 end of the exumbrellar groove in which it lies (1915). And these pads, being 

 tough and resistant, are sufficiently preserved to show that in this respect the 

 present specimens agree exactly with the type. Nor is there any difference in 

 the structure of the tentacles, which are smooth distally, their outer parts 

 ringed with nematocyst ridges, without suckers, but terminating in nemato- 

 cyst knobs. It is not possible to count the tentacles in either specimen, but 

 to judge from their number in such small segments of the margin as are intact, 

 there must have been 80-100, i.e., about the same number as in the type speci- 

 men. 



Only a few otocysts are still to be seen. But fortunately such as remain 

 are large enough to show that they lie in capsules, the various elements of which 

 are visible even in optical section, and imbedded and entirely enclosed in the 

 exumbrella, exactly as in the original specimen of Eperetmus. In fact the figures 

 of the margin of the latter (1915, pi. 59) would equally apply to the present 

 material. The sense organs themselves are spherical, with central otocyst 

 mass, borne on a stalk. 



In all this our specimens agree perfectly with Eperetmus typus. But it is 

 impossible to determine whether one of the most important characters of the 

 latter, the presence of centripetal canals, recurs here. In their present state 

 the specimens show no clear evidence of them, though in the case of the smaller 

 one the circular canal in one interradius is apparently dilated centripetally . 

 But, considering the macerated and rubbed state of the subumbrella, it is an 

 open question whether such canals were really absent, or whether their apparent 

 lack is merely the result of mutilation, as so often occurs with these structures 

 in Liriope. And it is the necessary uncertainty on this point which makes their 

 identity with Eperetmus typus doubtful, a doubt which cannot be cleared up 

 till larger and better preserved series are available. 



So close is the resemblance between the Port Clarence specimens and the 

 one known specimen of Eperetmus, even to the most minute details of structure 

 of the marginal organs, that such divergence as lack of centripetal canals in 

 the former, would be a somewhat surprising phenomenon. And should it prove 

 that they are really absent in fact, as well as in present appearance, the generally 

 accepted classification of the family would demand for them not only a new 

 species but a new genus. 



Family TRACHYNEMID^E Gegenbaur. 



Aglantha digitale (Fabricius). 

 Medusa digitale Fabricius, 1780, p. 366. For Synonymy, see Mayer, 1910, p. 402. 



Specimens of this well-known species, all rather fragmentary, were taken at: 

 Stations 21 a, 6, c, lat. 68 30' N., long. 166 32' W., August 15, 1913. 

 Stations 256, c, off Cooper island, Alaska, surface, August 27-28, 1913. 



