196 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



ties with A. wyvillei, A. bairdii, and A. verrillii. Thus the margin 

 of its central lens is irregularly notched as in A. wyvillei, but without 

 radial furrows. There is an annular ridge upon the outer side of 

 the ring- furrow, and the outer edge of this ridge is simple and entire, 

 as in A. bairdii, in about two-thirds of its circumference, and notched 

 as in the typical A. giantea in the remaining one-third. The central 

 lens is more than half as wide as the medusa, as in A. bairdii, A. 

 verrilli, and A. valdiviae. 



It is evident that intergrading conditions prevail to a hopeless 

 degree among many of the so-called "species" of Atolla. In fact, 

 I think there are but two well-distinguished species: A. bairdii with 

 smooth exumbrella and A. chuni with well-developed and quite regu- 

 larly arranged papillae upon the exumbrella sides of the lappets. 

 As a matter of convenience, however, we may distinguish A. bairdii 

 var. wyvillei by the notched margin of its central lens, and the ab- 

 sence of a well-marked annular ridge on the outer side of its coronal 



furrow; for while there is often an annular 

 ridge on the outer side of the ring-furrow, 

 the margin of the central lens usualty pro- 

 jects over it, overarching and concealing it 

 from view. A. bairdii is a case where this 

 ridge is so well developed that it projects 

 var. wyvillei from the beyond the margin of the central lens. 



Philippines Gulf op g 35 spec i mens f Atolla Were found 



Bon 1 ; depth, 492 fath- r 



oms. by the Albatross among the Philippine 



Islands; and of these 18 are more or less typical A. vjyvillei, 4 are 

 intermediate in condition between A. wyvillei and A. alexandri, 3 

 are intermediate between A wyvillei and A. bairdii, 1 combines the 

 characters of A. bairdii with the forma valdiviae. 



The specimen of Atolla gigantea, Cat. No. 28690, U.S.N.M., which 

 shows affinities with A. bairdii and A. verrillii, was dredged at Sta- 

 tion D. 5647, from Buton Strait, about 11.6 miles off North Island, 

 depth 519 fathoms, bottom green mud. This medusa is a large one, 

 being 130 mm. wide and with 29 tentacles. The diameter of the cen- 

 tral lens is 94 mm. and the thickness of its gelatinous substance 21 

 mm. The margin of the central lens is irregularly notched, but is 

 without distinct radial furrows. Its margin overarches the ring- 

 furrow, which is 15 mm. deep. The outer edge of the ring-furrow 

 exhibits an annular ridge, which is, however, overarched and hidden 

 under the projecting margin of the central lens. Two-thirds of the 

 circumference of the peripheral edge of this annular ridge is entire 

 and plain, as in A. bairdii, but about one-third of it is notched, the 

 notches tending to lie in the radii of the tentacular pedalia. as in 

 the typical A. gigantea. 



