MARGELIS CAKOLINENSIS. 



157 



the bell is almost spherical ; the tliickness of the disk is so great that 

 the cavity of the bell only extends to half the heii^ht of the vertical 

 axis. (See Fig. 241.) 



In young specimens (one tenth of an inch in height) just liberated 

 from the Hydromedusarium, the outline of the disk is bell-shaped (Fig. 

 244), the cavity of the bell is lai-ge in i)i()})()rti()n. and the thickness of 

 the upper part of tlie bell is not one third of tlie height of tiie actinal 

 axis. The digestive cavity and tlie ])eduncle are one ; it is bottle- 

 shaped, cylindrical, and not yet divided by four longitudinal riirrows 

 into genital pouches. These small Medusae have, like the young of 

 Bougainvillia, when freed from the Hydi-omedusarium, but two tenta- 

 cles at the base of each of the chymiferous tubes (Figs. 244, 245), the 



Pip. 245. 



digestive cavity terminates likewise with perfectly simple, stift' oral ten- 

 tacles, w^hich begin to branch only in somewhat more advanced stages. 

 The generic identity of Bougainmllia britannica with our Margelis 

 caroUnensis is perhaps not better shown than by the agreement of the 

 young Medusa3 in all their essential features, while the Hydrarium shows 

 that the specific difference between the English and American rejjresen- 

 tatives is not to be questioned. See the observations of Dalyell on the 

 development of his Tubularia ratnosa, PL XL Vol. I., Animals of Scot- 

 land, and the figures of Hodge of Podocoryne Alderi. which I presume 

 is only a young of one of the species of Bougainvillia (Margelis Steenst.) 

 of Forbes. It seems therefore perfectly justifiable to reconstruct the 

 genus Bougainvillia in such a way as to separate from it those species 

 W'hich have a long, slender digestive cavity, with but slightly branching 

 tentacles, under the name of Margelis. 



The oral tentacles are, in the youngest Medusae (Fig. 244), small. 



Fig. 244. Young Margelis, having only two marginal tentacles at the base of each chymil'erous 

 tube, and simple oral tentacles. 



Fig. 245. Young Margelis, seen from the abactinal pole, in the condition of Fig. 244. 



