NEW FORM Oi - NAKED-EYED MEDUSA. 39 



rather higher than midway between the marginal riug and the 

 convex surface of the disk. The depth of the concavity lessened 

 during contraction, but not uniformly so, it being observed that 

 the upper part remained unaffected to the extent of a third of its 

 area, from the summit downwards, forming, as it were, a point 

 d'appui for the development of contractile action throughout the 

 remainder of the membrane. The proboscidiform peduncle has all 

 the features common to the genus. The gastro-wascular canals — 

 four radiating and one circumferential— contain two kinds of 

 corpuscles ; the smaller are rather less in diameter than human- 

 blood globules, while the larger, apparently mother-cells, are 

 nearly three times greater, possessing nuclei of variable size, but 

 frequently identical in character with the lesser corpuscles. They 

 moved in a moderately rapid and regular manner, their course in 

 the radiating vessels being continuous from one half of the hemi- 

 sphere to the other. Thus, two vessels carried the particles from 

 the marginal canal, convergingly, to the central point of inter- 

 communication, on the one hand, and two conveyed the same 

 elements from the centre, divergingly, on the other. The repro- 

 ductive glands, four in number, elongated or semiclavate, are placed 

 on the inferior surface of the sub-umbrella, a short Avay distant 

 from the margin, and in the course of the radiating canals. Each 

 gland was subdivided by one of the radiating vessels traversing its 

 long axis. The subjacent ova at the surface generally displayed 

 an outer cell-wall, with its included transparent albumen, a second 

 membrane surrounding tbe molecular yolk, and a third consti- 

 tuting the germinal spot, within which were three or four rounded 

 particles, beautifully distinct. Deeper in the organ were similar 

 cells, smaller in size and imperfectly developed, evidently destined 

 to supply the place of those ripe for expulsion. 



To facilitate identification, it may be remarked tbat Thauinantias 

 inconspicua has the disk wider and more flattened, purplish- 

 coloured glands and twenty tentacles. T. punctata has thirty- 

 two tentacula, and is a larger species, with the umbrella more 

 depressed, and T. Thomsoni has but sixteen tentacula. There is 

 no other British species for which Thaumantias achroa can be 

 readily mistaken. 



