128 DISCOPHORiE. Part III. 



SECTION III 



DESCRIPTION OF PELAGIA CYANELLA. 



Eeturning, now, to the Pelagidas observed along the Atlantic coast of North 

 America, I have only to notice two species, one of which, the Pelagia cyanella, is 

 represented on PI. XII. of the third volume, while the other has not j^et been 

 figured. Our Pelagia cyanella has already been accurately described by Eschscholtz, 

 but a figure with details of its structure was still wanted, and I have attempted 

 to supply the deficiency. Like Pelagia noctiluca, which is its European represent- 

 ative, our Pelagia cyanella is remarkable for the striking rotundity of its umbrella, 

 the margin of which is usually more contracted than the middle of the disk. 

 Fig. 1. The whole of the surface, but especially the middle space, is dotted with 

 little reddish-brown warts, arranged in radiating lines. The prevalent color of the 

 whole disk, and of the arms, is bluish white, hyaline, through which shines reddish- 

 brown pigment {Fig. 3) in the marginal sacs of the radiating pouches, and along 

 the whole length of the tentacles, which are of a more brick-red color, while the 

 ovaries shine through with a more purplish tint; upon the outer surface of the 

 pendant arms there are reddish-brown dots, as upon the outer surface of the um- 

 brella. The tentacles are capable of very great elongation and contraction, hanging 

 at times far beyond the actinostome, while at other times they are shortened to 

 a length less than the diameter of the di.sk. The actinostome consists of a slender 

 peduncle, formed by eight pillars {Fig. 2, a), alternating with the main lobe {b) of 

 the genital pouches, and uniting into a cylinder, which divides again into four long 

 slender arms {Fig. 1, s) with thin lobulate margins. This specimen was observed 

 in the Gulf of Mexico, at the Tortugas Islands, and an opportunity was offered 

 to trace some stages of its development, embracing five days, beginning at the 

 time when the imperfectly developed young, having the appearance of a planula or 

 of an imperfect scyphostoma {Fig. 4), were seen dropping frona its actinostome. The 

 embryos corresponded in their structure to those of Cyanea arctica represented on 

 Plate X. Fig. 12, without, however, showing the slightest inclination to attach them- 

 selves to the ground. They soon presented a wider excavation (PI. XII. Figs. 5, 6, 

 and 7), approaching to the condition of Cyanea represented in PI. X. Fig. 13, and 

 on the third day, PI. XII. Figs. 8 and 9, the beginnings of eight tentacles {h) were 

 unmistakable, and the mouth appeared like a distinct opening in the centre {a). 

 In this stage the young Pelagia may be compared to the scyj)hostoma of a Cyanea 

 which is already attached (PI. X. Fig. 14), and yet the Pelagia remains free, and 



