﻿April, 1857.] 



ELLIOTT SOCIETY. 



193 



Larva unknown. 



Distribution. — Charleston Harbor. 



PHORTIS GIBBOSA, nov. spec. 



The thickness of the disk above the digestive trunk does not 

 fall far short of its width across the tentacular circle, except when 

 .the animal is much expanded. The curvature of the outline from 

 the summit to the margin is not the arc of a circle, but rather para- 

 boloid. The projection downwards of the disk-substance which 

 gives attachment to the digestive trunk is so large as to occupy a 

 very considerable portion of the cavity, converting it, indeed, into 

 a sort of circular fossa, (as in Tima,) whose outer wall is much 

 more steep than the inner. However this prominence does not 

 reach the level of the vail, but gives attachment within the vail 

 to a rather large digestive trunk, which hangs without the vail, 

 and this carriage appears to be habitual. The sexual organs, 

 quite elongate in large specimens, occupy nearly all that portion 

 of the radiate tubes which traverses the steep side of the circular 

 fossa representing the bell-cavity. They thus lie near the mar- 

 ginal tube but do not reach it. Though not pyriform, they grow 

 rather larger as they approach the margin. The tentaculum is 

 provided with a rather globular bulb and a slender and very ex- 

 tensile lash. The number of these organs varied among my few 

 specimens from twelve to fourteen, probably sixteen is the highest 

 number ever attained, and this only in cases of deformity by 

 excess. Between the tentacula are found a variable number of 

 tubercles bearing thread-cells and marginal capsules, which I 

 have noticed in the diagnosis of the genus, though by no means 

 certain that the number of these should not rather be included 

 among specific characters. 



Uninjured specimens of this species are by no means so clumsy 

 in their motions as might be supposed from their heavy appear- 

 ance. Though the disk-cavity is so very shallow, and though, 

 from the excessive thickness of the disk-wall in its upper part, 

 only a limited portion of it appears to be concerned in giving an 

 impetus to the water, yet this is done with sufficient force and 

 frequency to impart celerity and an air of liveliness, which makes 

 an interesting contrast with the heavy form of the species. 



My specimens of this species have all been taken in August. 

 It is the largest Naked-eyed Medusa in our waters with the ex- 

 ception of the two species of Eutima. 



