LUCERNARIDiE. 493 



the digestive cavity. The space between the polypite-wall 

 and the inner surface of the cup is equally divided. A 

 circular sinus has its course beneath the insertion of the 

 tentacles. By means of a band of muscular fibres which 

 transverse its margin, and another set which radiate 

 towards the polypite, the distal extremity of the cup can 

 be folded or drawn inwards. It has been observed to 

 detach itself, and swim in an inverted position by the 

 slowly repeated movements of its cup-like umbrella, thus 

 resembling Pelagia, a more active and permanently free 

 member of the same order. 



Three families of the beautiful Lucernaridse, all of 

 which are at once distinguishable by their umbrella, may 

 be defined as follows : — 



Family 1, Lucernaridse. Reproductive elements de- 

 veloped in the primitive hydrosoma, Avithout the inter- 

 vention of free zooids. Umbrella with short marginal 

 tentacles and a proximal hydrorhiza. Polypite single. 

 Family 2, Pelagidse. Reproductive elements developed in 

 a free umbrella, which either constitutes the primitative 

 hydrosoma, or is produced by fission from an attached 

 Lucernaroid. Umbrella with marginal tentacles. Poly- 

 pite single. Family 3, Rhizostomidae. Reproductive ele- 

 ments developed in free zooids produced by fission from 

 attached Lucernaroids. Umbrella without marginal ten- 

 tacles. Polypites numerous, modified, forming with the 

 genitalia a dendriform mass depending from the umbrella. 



For a further description of this interesting species see 

 Professor Miiller's paper, Journal of Microscopical Science, 

 vol. iii. p. 265 ; or, Professor Greene's Manual of the 

 Coelenterata. 



The flat circular horny disc forming the skeleton of 

 Propita gigantea, to the naked eye exhibits both radiating 

 and concentric markings ; and, when examined with a 

 power of 40 diameters, its upper surface is found to be 

 furrowed, and two rows of small projecting spines occur 

 upon the ridges between the furrows, the ridges being the 

 radiating fibres above noticed. The under-surface, or that 

 to which the greater portion of the soft parts of the 

 animal are attached, is more deeply furrowed ; and plicae 

 or folds of the mantle fit accurately into the furrows, from 



