SEMAEOSTOME^ — AURELLIA. 627 



Aurellia aurita forma "inarginalis." 



Aurelia miirginiilis, Agassiz, L., 1862, Cent. Nat. Hist. U. S., vol. 4, pp. 86, 160.— Agassiz, A., 1865, North Amcr. Acal., p. 43.— 

 Haeckei., 1880, Syst. dcr Mcdusen, p. 556.— Hvde, 1894, Zeit. fiir wisscn. Zool., Bd. 58, pp.532, 544, taf. 32, 33, 

 fign. 1-35. 



This variety is larger than A. flnviJtila, being often more than 300 mm. in diameter. 

 Mouth-arms smaller than in .7. flaviilulii, being less than bell-radius in length. Genital 

 pouches fully half as wide as bell-radius, instead of being about one-third this width as in 

 A. flavulula. The gonads are of a pale rose color in both sexes. 



Professor Hyde has made a careful study of the development up to the scyphostoma 

 stage. The gastrula results from a peculiar process of delamination. Some of the cells of 

 the one-layered blastula divide and their inner halves thus become free and wander into the 

 blastula cavity where they eventually form the entodermal layer. 



According to Hyde, however, the development of A. finvidiila is itself subject to much 

 variation and the gastrula in this form also results in some cases from delamination. Hence 

 the peculiar features ot the development in A. marginalis are different only in degree from 

 those observed by Hyde in A . jlavidida and are not of specific importance. Moreover, we 

 must bear in mind that Smith finds that the gastrula oi Aurellia flavidula is formed by invagina- 

 tion, and according to Gtitte and to Hein, 1900, the gastrula o( A. aurita is also formed by 

 invagmation. Staleness of the water in ordmary aquaria may profoundly alter the normal 

 course of development. 



I am convinced that "Aurellia marginalis" is only a variety of"//, flavidula," which is 

 itself specifically identical with A. aurita. For example, among 27 mature specimens of 

 Aurellia found in a single swarm at Tortugas, Florida, on May 4, 1906, if we call r the radius 

 of the umbrella, the length of the mouth-arms ranged from 0.89 to 1.04 r, the average being 

 0.95 r; also the radius of the genital cross ranged from 0.36 to 0.51 r, the average being 0.42 r. 

 Agassiz called specimens of Aurellia with arms longer than r and the genital radii less than 

 0.5 r "A. flavidula"; those having arms less than r and genital radii more than 0.5 r he 

 would call "A. marginalis." It is evident, however, that the two forms intergrade, and this 

 is true not only along the Florida reef, but also in the harbor of Eastport, Maine, where I 

 found some individual Aurellias that conform to the proportions o("A. marginalis." It is 

 safe to conclude that "A. marginalis" is merely a manuscript species and should disappear 

 henceforth. L. Agassiz described it from the Florida reefs. 



Aurellia aurita = "Aurellia dubia" Vanhoffen. 



Aurelia dubia, Vanhoffen, 1888, Bibliotheca Zoologica, Bd. i, Heft. 3, pp. 20, 24. 



The disk is 130 mm. wide and 43 mm. thick. The 8 marginal sense-organs are set in 

 deep niches, as in A. flavidula, and there are 8 broad, marginal lappets. The 8 mouth-arms 

 are only two-thirds as long as the disk-radius. Genital-radius one-third of disk-radius; 7 

 radiating canals extend outward from each genital sinus. All of the canals fork; their branches 

 are narrow and elongate in the middle and small and numerous at the margin. Color (?) 

 Persian Gulf, March. 



Described from a single specimen by Vanhoffen. Distinguished by its short mouth- 

 arms and its having only 8 velar lobes instead of 16 as in A. lahiata. 



Aurellia solida Browne. 



Aurelia solida, Browne, 1905, Fauna and Geog. Maldive and Laccadive .\rchipeIagoes, vol. 2, plate 960, plate 94, figs. I, 2; 

 1908, Trans. Royal Soc. Edinburgh, vol. 46, p. 249. 



This medusa differs from Aurellia aurita in its marginal sense-organs, but in all other 

 respects the characters of A. solida are well within the common ranges seen in A . aurita. In 

 Aurellia solida each marginal sense-organ arises from the inner end of a deep groove 

 which is open on the exumbrella side and bordered by the lateral lappets, but closed on the 

 subumbrella side. In Aurellia aurita the sense-club points outward toward the umbrella 

 margin. In Aurellia solida, however, the sense-club points upward toward the exumbrella 

 and therefore at right angles to the position assumed by the sense-club in Aurellia aurita. 



In Aurellia aurita there is a well-developed covering membrane or "hood" which extends 

 over and above the sense-club on the exumbrella side, but in Aurellia solida the "hood" is a 



