﻿April, 1857.] 



ELLIOTT SOCIETY. 



197 



are each connected with the bulb of a tentaculum, being placed 

 beneath and somewhat on one side of it. Should this position be 

 not constant for adult specimens of all the species, it may be ne- 

 cessary hereafter again to sub-divide the genus. 



The larvae are those Campanularidas which have a rather shal- 

 low cup with an entire rim, and the horny vesicle of the budding 

 polyps not transversely divided into annulations. When the me- 

 dusas first escape from their nurstsries, the disk is small and more 

 or less reverted, the mouth not infrequently simple, the tentacula 

 few in number, twelve or sixteen, and the eight marginal capsules 

 considerably distant from their bases. Also the sexual organs 

 are either entirely indistinguishable, or barely traceable near the 

 base of the prominent digestive trunk. The Medusas referable to 

 this genus appear never to attain a large size. 



Distribution. — Seas of Norway, Holland and Great Britain, the 

 Mediterranean and Charleston Harbor. 



OBELIA COMMISSURALIS, nov. spec. 

 PI. 11, Ff. 5-7. 



The general form is not so flat as that of Thaumantias plana 

 Sars, but when viewed in profile the outline is seen to project 

 slightly at the summit of the disk, producing the form of a 

 cone with very low altitude and very broad base. From the 

 periphery of this base projects downward the lower part of the 

 wall of the disk, like the upturned peripheral edge of a watch 

 glass. The digestive trunk descends nearly to the level of the 

 vail. The nearly round sexual organs are situate quite near the 

 marginal tube. The transverse diameter of these organs exhibits 

 a tendency to diminish towards the marginal tubes. Fig. 6 gives 

 a striking instance of this. The largest number of tentacula 

 counted in any specimen has been thirty-two, but I feel satisfied 

 that the number in specimens attaining full maturity in their 

 native element will be found to be much greater, especially since, 

 even in this instance, new tentacula were springing up between 

 the old ones. The tentacula are short and of stiff carriage, being 

 borne nearly straight for about two-thirds their length from the 

 bulb, and curved or hooked for the remainder. 



The larva of this Medusa is a small, delicate, and in fall and 

 winter much branched Campanuiaria, growing between tide- 

 marks on Bowman's Jettee, Sullivan's Island. In spite of its 

 abundance fully grown Medusas are seldom taken with the dip-net. 



