UHIZOSTOM.E — COTYI-OUHIZA, POLYRIIIZA. 603 



Stage there are still only 24 lappets, 16 rhopalar and 8 velar. When 4.5 to 5 mm. in diameter 

 the ephyra has 8 (4 pairs) ot 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 of the single-mouthed ScyphomedusK 

 and that only later it acquires the characters of the multi-mouthed Rhizostomx. This is 

 true ot all known ephyra 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 (lotylorliiza the reader should consult the papers 

 ot Claus, Goette, Hein, and Kowalevsky. 



Bouvier, 1907, finds T rochurus to be commensal with this medusa. 



Haeckel's Cotylorhtza ambulacrata described from a preserved specimen from Lessona, 

 Canary Islands, Atlantic Ocean, appears to me to be identical with C. tuhcrculatn, being well 

 within the limits of variation of the t\pical medusae found at Naples. 



Genus POLYRHIZA L. Agassiz, 1862. 



Polyrhiw, Agassiz, L., 1S62, Com. Nat. Hist. U. S., vol. 4, p. 156.— Haeckel, 1880, Syst. dcr Mcduscn, p. 576.— Vanhoffen, 

 1888, Bibliotheca Zoologica, Heft. 3, p. 40. — Maas, 1903, Scyphomedusen der Sibogn Expedition, Monog. 11, pp. 32, 81. 



GENERIC CHARACTERS. 



Rhizostoiiiata duhotoma with mouth-arms bifurcated two or more times. Exumbrella 

 without a dome but 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. 



Homopnciiiii fronJosa Lesson and Oryt/mi tncrAor Quoy and Gaimard are believed by 

 Haeckel to belong to the genus Pol\rhiza, but the descriptions and figures of these medusae 

 are so vague, fanciful, and evidently inaccurate that we can not consider them. (J)ne should 

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

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

 these are moUusca). 



Polyrhiza vesiculosa L. Agassiz. 



Cephea vesiculosa, Ehrenberg, 183E;, .Abhandl. Berlin .Acad., p. 260. 



Polyrhiza vesiculosa, Agassiz, L., 1862, Cont. Nut. Hist. U. S., vol. 4, p. 156. — Hamann, O., 1881, Jena.Zeit. fijr Naturw.,Bd. 15, 

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



Bell 50 to 60 mm. wide, flat, with a pit at center of e.xumbrella. 32 dichotomous, radiating 

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

 exumbrella. 8 rhopalia. 80 lappets, hi each octant are 8 rectangular velar and 2 small 

 rhopalar lappets. The mouth-arms branch dicbotomously 4 to 6 times. There 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 h\' 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 Vanhijffen, sensu Maas, 1903. 



Rhizostomata triptera+ R. trigona, Vanhoffen, 1888, Bibliotheca Zoologica, Bd. I, Heft. 3, pp. 41, 44. 

 Rhizostomata triptera, Maas, 1903, Scyphomedusen der Sihoga Eiped., Monog. 11, 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 powerful and the radial-muscles weak. 



There is no sharp line of demaikation between the Rliizostotnala dichutomn with mouth- 

 arms V-like in cross-section and the Rhizostomata tnptera wherein the arms are Y-shaped in 



