1(III7.0ST<>M.K COTYLOKHI/A, POLYRHIZA. 



stage there are still only 24 lappets, 16 rhopalar anil S velar, When 4.5 to 5 mm. in diameter 

 the ephyra has 8 (4 pairs) of cleft mouth-arms and the ring-canal has become unrecognizable, 

 owing to the fusion into a network of numerous, lateral vessels which arise from the 16 radial- 

 canals. It is evident that at first the ephyra is like that ot the single-mouthed Scyphomedusz 

 and that only later it acquires the characters ot the multi-mouthed Rhizostomae. This is 

 true of all known ephyrae of the Rhizostomae, and it furnishes the strongest argument for the 

 theory that the Rhizostomae have been derived from the more simply organized, single- 

 mouthed Scyphomedusae. 



For further details of the development of (.'ntylni luzn the reader should consult the papers 

 of Claus, (joette, Hein, and Ko\vale\sk\ . 



Bouvier, 190", finds Tnii-linrus to he commensal with this medusa. 



Haeckel's Cotylorhiza ambulacrata described horn a preserved specimen trom Lessona, 

 Canary Islands, Ailantic Ocean, appears to me to he identical with (1. tnli,-r. nlnt.i. heing well 

 within the limits of variation of the typical medusae found at Naples. 



Genus POLYRHIZA L. Agassiz, 1862. 



Polvrhisa, AGASSIZ, I.., 1862, Cont. Nat. Hist. I'. S., vol. 4, p. l 56. HAFTKEI., 1880, Sv-i. ,|IT Mc.luvcn, p. ^-d. Y*MiiJ> fr.N, 

 1888, Bibliothcca Zoologica, Hcfi. 3, p. 40. M**s, i:>o\, Scyplinini-ilusrn di-r Siboga Eipr.lition, Mmm!. 1 . 1 1, pp. 32, 81. 



GENKRIC CHARACTI KS. 



Rhizostomata Jicliototnn with mouth-arms hifurcated two or more times. Exumbrella 

 without a dome hut with a central concavity and with radiating furrows. Numerous simple 

 filaments between the mouths. 8 rhopalia. Numerous radial-canals and a wide marginal 

 network of vessels. 



Homopneusis fronJosa Lesson and Orythia in<:<il<ji Ouoy and Gaimard are believed by 

 Haeckel to belong to the genus Polyrhiza, but the descriptions and figures of these medusa; 

 are so vague, fanciful, and evidently inaccurate that we can not consider them. One should 

 consult Lesson, R. P., 1829, Voyage de la Cotjiiillf, Mollusques, plate 12; and Ouoy et 

 Gaimard, 1833, Voyage d YAstrolabe, Zoophytes, tome 4, p. 297 (not plate 25, figs. 6 to 10; 

 these are mollusca). 



Polyrhiza vesiculosa L. Agassiz. 



Ceflira resiculosa, EHRFNBF.RG, 1835, Abliamll. Bcvlin AcaJ., p. 160. 



Pol \rhiza vcsiculosa, AC.ASSIZ. I.., 1862, Cont. Nat. Hist. U. S., vol. 4, p. l 56. HAMANN, O., 1881, Jena. X.i'ir . fur \,iumv.,BJ. i ;;, 

 p. 247, taf, 9, fig. 7 (anatomy of mouth-arms). 



Bell 50 to 60 mm. wide, flat, with a pit at center of exumbrella. 52 dichotomous, radiating 

 furrows are separated by a deep annular furrow from the equally wide marginal zone of the 

 exumbrella. 8 rhopalia. 80 lappets. In each octant are 8 rectangular velar ami l small 

 rhopalar lappets. The mouth-arms branch dichotomously 4 to 6 times. I here is a large 

 cluster of long, simple filaments at the center of the arm-disk. 32 radial-canals, 8 large 

 rhopalar and 24 narrower canals, all connected one with another by a wide-meshed network 

 of anastomosing vessels. There is no definite ring-canal. 



Bell rose-red, knobs of mouth-tentacles brownish-black. Filaments transparent. Found 

 in the Red Sea, at Tur and Suez. 



RHIZOSTOMATA TRIPTERA Vanhbffen, sensu Maas, 1903. 



Rliizostomata lriflera+ R. trigona, VANH"> ft N . tNSS, Bihh. .tin > .1 /.. il ifii .1. B.l. i. Hi-fi. ;. pp. 41, 44- 

 Rhisoslomala Iriftrra, MAAS, H)O',. Si \ phoim \lusra ilcr Siboga Elpi'.l.. M"ii"i;. II, p. 46. 



Rhizostomae in which the lower parts of the 8 separate mouth-arms are 3-winged or 

 Y-shaped in cross-section, being expanded in a ventral and 2 dorsal lamellae. The 3 lamellae 

 narrow outwardly and meet in a point at the lower end of the arm. The frilled mouths are 

 borne upon the 3 lamellae, especially along their free edges. The mouth-arms do not bear 

 scapulets. The ring-muscles of the subumbrella are pn\\< iliil and the radial-muscles weak. 



There is no sharp line ot demarkation between the Rhizostomata dichatoma with mouth- 

 arms V-like in cross-section and the Rhizostomata trif>t,-ni wherein the arms are Y-shaped in 



