﻿April, 1857.] 



ELLIOTT SOCIETY. 



143 



cavity is colored like that of Chrysomitra. At this stage of growth 

 and with no trace that I could find of sexual organ, these buds 

 became detached from the medusa-bearing polyps and sunk in 

 clouds to the bottom of the vessel in which the larva was con- 

 tained. This 1 believe to have been abnormal, for the bell-cavity 

 was yet unopened and the buds consequently motionless. I sup- 

 pose the premature fall to be due to the rough handling all the 

 specimens I have seen, had received. 



The buds at their first appearance were colorless. It will be 

 seen from the foregoing description that the development of the 

 disk in this genus is strictly according to the Endostome or closed 

 manner. The larval community of Porpita is distinguished from 

 that of Velella or Chrysomitra by having its air-shield circular 

 and without a vertical crest. Its marginal tentaculiform individu- 

 als also are provided with three rows each of knobs along their 

 sides. 



No doubt as we increase our knowledge of the Medusa-forms 

 of these species, Porpita will be sub-divided into new genera. 

 Thus P. gigantea probably constitutes a new type with its nu- 

 merous marginal individuals and their sessile knobs; while the 

 distinction made by Lesson between the species with white and 

 blue shields is probably founded upon structure, and therefore a 

 good generic distinction. It may be due to the blue-disked spe- 

 cies having the mantle prolonged upwards over the white shield. 

 In that case, perhaps, Polybrachionia, a name given by Lands- 

 down Guilding to a Carribbean species, might be retained for one 

 of the groups. The species following belongs to the white-disked 

 group. If I am right in my conjecture that Lesson's Ratis and 

 Acies are types of two stages in the growth of this larval com- 

 munity, the following would be the method : First, a small free 

 polyp having a conical mouth and digestive cavity, and, like Eu- 

 ♦ dendrium, a single whorl of tentaculiform organs; an air-shield 

 which is small and fleshy, not fibro-cartilaginous, placed on the 

 base of the polyp. At this stage there are no medusa-bearing 

 individuals. This corresponds to the Acies of Lesson. Next, the 

 polyp which was originally as great in diameter as the shield, is 

 now become, by the growth of the shield, relatively less, and 

 within the row of marginal tentaculiform individuals a few medu- 

 sa-bearing polyps have appeared. This stage would be Lesson's 

 genus Ratis. Now this is the order of growth among the corres- 

 ponding parts in our next group, the Tubularidte, and I think such 



