MARGELIS. 155 



of uniform thickness, the veil large and powerful ; Fig. 239. 



the abactinal portion of the bell becomes somewhat 

 more thickened, and when it has separated from 

 the Hydrarium (Fig. 238), the tentacles far exceed 

 in length the diameter of the bell, the sensitive 

 bulb (Fig. 239) having become quite well defined 

 in outline ; it is somewhat quadrangular, filled with 

 dark pigment cells, p, and at the base of each tentacle a bright eye- 

 speck, e, is formed ; the club-shaped oral appendages soon Fig 

 begin to branch, additional tentacles appear in pairs on each 

 side of the original pair (Fig. 240), and the young Medusa 

 soon assumes all the principal features of the adult, as in Fig. 

 232, with the exception of the simpler character of the ten- 

 tacles of the actinostome. 



Massachusetts Bay (Agassiz). 



Cat. No. 27, Nahant, Mass., Sept. 1854, H. J. Clark. Hydrarium. 



Cat. No. 28, Beverly, July, 1861, A. Agassiz. Hydromedusarium. 



Cat. No. 29, Nahant, July, 1861, A. Agassiz. Hydrarium. 



Cat. No. 30, Newport, R I., Prof. J. Leidy. Hydromedusarium. 



Cat. No. 31, Newport, R L, S. Powell. Hydromedusarium. 



Cat. No. 408, Nahant, July, 1862, A. Agassiz. Hydromedusarium. 



Cat. No. 447, Nahant, July, 1864, A. Agassiz. Hydromedusarium. 



Museum Diagrams, Nos. 20, 22, after A. Agassiz. 



MARGELIS STEENST. 



Margelis STEENST.; in Vidensk. Meclel. for 1849-50, p. 43. 

 Margelis AGASS. Cont. Nat. Hist, U. S., IV. p. 344. 18C2. 

 Bougainvillia LESS.; in Ann. Sc. Nat., V. 1836. 

 Hippocrene McCn. (nee Mert. nee Agass.). Gymn. Charl. ILirb., p. 61. 



The structural differences observed in the European Bougainvillia 

 britannica Forbes, and the Hippocrene, carolinensis McCrady, seem 

 sufficient to separate them from the genus Hippocrene, as has been 

 proposed by McCrady. The digestive cavity, instead of being a short, 

 rounded sac, attached at some distance below the highest point of 

 the chymiferous tubes, is long and slender, swelling slightly towards 

 its actinal end, and attached at the point of junction of the chymif- 

 erous tubes ; the peduncle of the actinostome is long, the oral tenta- 

 cles branch only two or three times ; these are more than specific 

 differences ; they are structural differences, unlike the differences we 

 find between species of the genus Bougainvillia, as between the 



Fig. 239. Magnified view of sensitive bulb. />, pigment-cells ; e, eye-speek. 

 Fig. 240. Tentacular bulb with the young tentacles, c, chymiferous tube ; 1, 2, 3, 4, different 

 sets of tentacles. 



