SH Canadian Arctic Expedition, 1913-18 



Station 27o: One specimen, contracted, of about the same size, from lagoon 

 inside Collinson point, Alaska, September 20, 1913; surface temperature, 30 F.; 

 ice, 5 inches thick. Catalogue No. 3292, Museum of Comparative Zoology. 



The type is in excellent condition, fully expanded except for the manubrium 

 and tentacles. In general out line it is high, bell-shaped, the subumbrella two- 

 thirds as deep as the bell is high; the gelatinous substance of the bell thick at 

 apex, thin at sides with smoothly rounded apex and no suggestion of an apical 

 projection (PL I, fig. 4). The surface of the bell is slightly, wrinkled in the type; 

 in the other specimen it is furrowed in the radii of the radial canals; but these 

 furrows are obviously contraction phenomena. 



The most interesting features of this new Medusa are the radial canals and 

 the tentacles. There are eight radial canals in each specimen, broad and 

 flat, all arising independently at the center of the apex of the manu- 

 brium (PL I, fig. 5). The four primary perradial canals are easily 

 distinguished, by their larger size, from the four of the second - 

 which alternate with them. But as all are equidistant, there is no evidence 

 that the latter originate as branches of the former, as occurs in the related 

 genus Bythotiara. The edges of all the radial canals in the contracted 

 specimen are smooth, with no traces of lateral spurs or branches, and though 

 they are slightly wavy in the type, this is apparently the result of muscular 

 relaxation, at least there are no definite lateral deverticula or spurs. And in 

 both specimens the edge of the circular canal is smooth, with no trace of even 

 such rudimentary centripetal spurs as occur occasionally in Heterotiara (Maas, 

 1905; Bigelow, 1909a, 1913; Hartlaub, 1913). 



Tentacles: The tentacles, best illustrated by the type owing to its relaxed 

 condition, are of two sorts, large and small, arranged as follows: opposite each 

 canal, and in each inter-radius, is a large tentacle; between these, a varying 

 number of small ones, of various stages in growth, from mere knobs to fully 

 developed ones (PL II, fig. 2). In four successive sixteenths of the margin of 

 the type these number 7, 7, 6, 6. The large tentacles, though agreeing with 

 the usual Calycopsid tentacle in the presence of terminal nematocyst knobs, 

 differ from those of Calycopsis, Heterotiara, etc., in being armed with ectodermic 

 nematocysts, arranged in rings, irregularly scattered, particularly over the 

 middle third of the tentacle. The large tentacles are, however, strongly con- 

 tracted, now (in the preserved state) being only 3-5 mm. long; hence, when 

 expanded, these nematocyst structures probably are less apparent, if visible at 

 all other than as scattered cells 



The large tentacles are hollow (PL II, fig. 1), as usual among Pandeidae and 

 Bythotiaridse but owing to their contracted state the lumen is very small. Their 

 relationship to the bell margin is the same here as in Calycopsis, the basal part 

 of each lying in a groove with the gelatinous substance of the exumbrella pro- 

 jecting downward between them (PL II, fig. 1). And it is also worth noting that 

 the marginal nematocyst ring is unusually thick, as compared with that of 

 related genera. 



The small tentacles differ from the large ones not only in size (being about 

 1.5 mm. long, and apparently not contracted), but also in structure, being 

 solid instead of hollow, with an endodermic core of large irregular chordate 

 cells (PL II, fig. 1). But, like the primary tentacles, they too bear terminal 

 nematocyst knobs, though otherwise without nematocysts. The small tentacles 

 exhibit every stage of growth, from mere bosses of the marginal ring to fully 

 formed tentacles, showing that their final number is not attained till a late 

 stage in growth, if, indeed, new ones are not developed as long as the Medusa 

 lives. But the largest ones are all of about the same size, and there is no 

 evidence that they ever develop further. That is to say, so far as the actual evi- 

 dence goes, it is safe to conclude that there is no intergradation between the twt 

 classes of tentacles. Small do not develop into large, but represent a distinco 

 series, really more cirrus-like than tentacle-like. 



I 



