2. Cephalites cumpanulatus. PL XIV. figs. 12 & 13. 



Plaits very deep ; increasing very rapidly from base, and dividing, 

 and so reduplicating, very constantly, both longitudinally and 

 transversely ; after attaining the fullest expansion, folding 

 inwards and downwards, and gradually contracting till they 

 more or less nearly approach the base, whence, folded upwards 

 in a single plait, the membrane rises, usually simple and 

 plain, in a funnel form, to the margin of the head surrounding 

 the central cavity, to which its marginal edge is attached : head 

 enwrapping the body and attached to all the prominent plaits 

 as far as the point where they incline rapidly towards the base : 

 diameter of body greater than height. 



This species differs very widely in outward appearance from 

 C. capitatus. In that species the head is indeed so largely de- 

 veloped as to be the most conspicuous part of the entire body ; 

 but it still leaves a view to some extent of the wall. In the pre- 

 sent species the whole fossil, unless actually looked at from be- 

 low, is so entirely enveloped by the cephalic membrane, rendered 

 necessary on account of the great depth and consequent tendency 

 to looseness of the fold, that no idea of the character of the 

 membrane of the wall itself can be gained externally. 



The modification of the fold is exceedingly remarkable, and 

 exceedingly difficult to be ascertained. The description given, 

 however extraordinary it may appear, is the result of very laborious 

 and careful examination, comparison, and section of all the spe- 

 cimens which I have been able to obtain. A familiar illustration 

 may perhaps assist in understanding the arrangement of this 

 membrane. If the inquirer will glance at the hangings of any 

 window, looped up, as usual, in festoons at some distance from 

 the ground by curtain pins or ropes, he will see a contrivance 

 rudely imitating the very elegant plan adopted by nature, to give, 

 in a small space, a very great extent of surface combined with 

 security to the polypiferous membrane of C. campanulatus. Take 

 a piece of linen cloth : join together the side-edges along their 

 whole length, gathering the lower edge to a point : fix the upper 

 end of the sac thus formed* to a circular plain wire : at a third of 

 the length from the bottom fix another wire, which, though alto- 

 gether uniting in a circle, is deeply zigzaged : the upper wire 

 remaining fixed, raise the lower wire equally all round, and so 

 that the drapery hanging from the upper simply circular wire 



* To act properly, and to give a full idea of the extent of surface gained, 

 the sac should be very much wider at the middle than at the top or bottom, 

 in order to fill the lower zigzaged wire and yet inclose the plain fold of the 

 cloth without compressing or touching it. 



