(After Bigelow, 1918; Kramp, 1926). Exumbrellar surface watch-glass shaped, subumbrella roughly flat; jelly thinning toward margin, markedly over peripheral 3-4 mm (Kramp) [Cyclocanna welshi ].
Radial canals four, narrow, following much-distorted S-shaped course (as seen from above), running from centre along perradius nearly to bell edge whence bending sharply to one side before running parallel with margin, eventually entering ring canal nearly 90° around bell from radius of origin (see illustration); junction with ring canal probably becoming increasingly remote from perradius of origin with advancing age (Bigelow), but in younger specimens junction being roughly interradial.
Gonads along most of length of radial canals, comprising broad, thin, vertically-hanging lamellae thrown into series of transverse folds; appearing widest in lateral view.
Manubrium wide, roughly cross-shaped in section but square in outline; appearing irregularly longitudinally wrinkled and folded in interradii in preserved specimens. Mouth broad, with undivided lip.
Marginal tentacles of two types, comprising just four small (when contracted) 'perradial' tentacles with much-swollen hollow bases, situated at marginal ends of radial canals, and in total probably up to ca 100 minute, short, papilliform hollow tentacles, varied in length, number increasing with age. Ocelli absent.
Bell diameter up to ca 70 mm. No other data available.
Interradial walls of manubrium (except lip and base) recorded dark violet (in life; dark grey to black in formalin), opaque. Perradii, in contrast, nearly pigment-free presenting striking pale-on-dark appearance in top view; rest of bell only lightly pigmented; undersides of four large marginal tentacles also lightly violet in life (blackish in formalin); stomach recorded also as dark violet (black in formalin).
Probably all known specimens of the species have been fertile; collected mid-August (off Chesapeake Bay, U.S.A.); mid-October (in mid-Skagerrak).
The few known specimens of the medusa have been taken in cool, deep, usually offshore water, but sometimes this has been close inshore (as at Bergen; Kramp, 1933). The Chesapeake Bay collection was from a haul from 140 m to the surface, that from the Skagerrak at 650 m depth.
Distribution around the British Isles
Not yet reported, but might occur in deep water to the west.
Distribution in the North Sea
Only known from the Skagerrak and near Bergen (summary in Kramp, 1961).
Known only from off Chesapeake Bay, U.S.A.
[After Cornelius, 1995a]