OF THE ACALEPHiE OF NORTH AMERICA. 355 



may vary, as the two lobes are pressed nearer together or stretched apart to a greater or 

 less extent. The modifications in this respect are ahnost endless, as also the manner in 

 which the margins of the lobes fold over; for their lower margin may hang loosely down, 

 as in Plate VII. Fig. 3, or it may bend inwards, curving itself in rounded or square 

 outline, as in Fig. 2, reaching, also, over the sides, or stretching more flatly. In these 

 various states of dilatation or contraction, the lobes may diverge from each other in 

 all possible degrees ; one may even overlap the other alternately, and thus reduce to 

 the utmost the difference between the longitudinal and transverse axis, as in Fif. 1. 

 The small lateral lobes, two in number on each side, may, in these various changes 

 of form, assume also the most diversified positions ; at times stretching straight down- 

 wards, at times arching upwards, at times hanging down, converging towards and even 

 crossing each other ; so that there is no end to the diversity of these aspects. I should 

 say, however, that the motions of these lobes, especially those of the two large anterior 

 and posterior lobes, arv. comparatively very slow and graceful; while those of the small 

 lateral lobes are somewhat more brisk. 



Seen from the sides, the pair of lateral ambulacra (Plate VII. Fig. 1 and 2) con- 

 verge from the upper summit towards the base of the lateral lobes, and the anterior 

 and posterior ambulacra of the same side appear in profile near the anterior and 

 posterior margin, encircling in parallel curves the lateral ambulacra, but extending 

 and gradually tapering all the way down to the lower margin of the lobes. 



The whole animal progresses rather slowly, its movements being tremulous, like dan- 

 cing in slow steps through the water, and now and then revolving upon itself. But we 

 never see those quick, darting motions which characterize Pleurobrachia, nor any thing 

 like the graceful curves of the tentacles following it like a comet's tail, for here the ten- 

 tacles do not extend beyond the margin of the lobes. And the lobes themselves are 

 an impediment to quick and graceful motion ; for the anterior and posterior ones are 

 disproportionate in size to the body. There is, however, an attitude in which the 

 movements of this animal are exceedingly graceful. It is when the lateral lobes are 

 fully expanded, and even recurved forwards and backwards, and so elongated as to 

 appear like two flower-petals spreading in an opposite direction, and curving outwards. 

 In this development the animal generally reverses its position, the mouth being turned 

 upwards, and the lateral lobes also curved outwards, presenting their vibrating fringes 

 in the utmost degree of activity, the whole animal resembling an open white flower, 

 with two large and four small petals revolving slowly upon its peduncle, or changing 

 its place in various directions. Fig. I. of Plate VIII. represents a specimen in such 

 an attitude. 



