RHIZOSTOM^ — MASTIGIAS. 681 



Mastigias pantherina Haeckel. 



Mmligias pantherina, Haeckel, i8So, Syst. dcr Mcjusen, p. 624— Vanhoki- en, 1888, Bibliothcca Zoologica, BJ. i, Heft. 3, 



p. 44; 1902, Wissen. Ergeb. Valdivia Exped., BJ. 3, Lfg. I, p. 49. 

 Mastigias papua, Maas, 1903, .Scyphomejusen Jer Sihoga Expcd., Monog. 11, p. 63. 



This is known only tiom a preserved specimen, briefly describeil by Haeckel. It appears 

 to be related to, if not identical with, M. ocrUata, having the same peculiar "e\e spots" on the 

 exumbrella. The velar lappets are said to be truncated and rectangular and to be more numer- 

 ous than in .1/. ocellata, there being 16 in each octant instead of about 12, as in M. occllatn. 

 Mouth-arms are much longer than in M. ocellata, being nearly as long as bell-diameter. The 

 simple upper part of the arm is hardl\' half as long as the 3-vvinged lower part, whereas in 

 M. ocellata and M. papua the upper part is longer than the lowest part of the arm. Terminal 

 club very much longer than in other forms of Mastigias, being 2 or 3 times as long as the 

 bell-diameter. 



Bell dark-brown with white spots ringed with black. Bell-margin black. 



Found at Samoa, tropical Pacific. 



Mastigias gracile. 



Desmostoma gracile, Vanhoffen, 1888, Bibliotheca Zoologica, Bd. 1, Heft 3, pp. 35, 45, taf. 4, fign. 5-7. 



Disk flatly rounded or hat-shaped, 35 mm. wide, thin at margin, but very thick at apex. 

 Exumbrella besprinkled with irregularly placed clusters of small warts. 8 marginal sense- 

 organs, the marginal lappets irregularly arranged, there being 5 or 10 rectangular velar lappets 

 in various octants; thus some marginal sense-organs may be close together, while others are 

 far apart. There is a wide, well-developed zone of ring-muscles, confined, however, to the 

 peripheral parts of the subumbrella, its inner edge being beyond the periphery of the arm- 

 p. liars. The subgenital ostia are twice as wide as pillars of the arm-disk. These ostia 

 appear double, thus gning the false appearance of 8 instead of 4 genital piis. This is due to 

 the fact that each of the 4interradial gonads is separated into 2 lateral ra\s b\' means of a cen- 

 tral gelatinous flap which divides the subgenital ostium into 2 side-openings. 



The 8 mouth-arms are hardly as long as the bell-radius and consist of a simple, short, 

 thick, upper part of the arm and an expanded 3-winged, lower part, which is 3 to 4 times as 

 long as the upper. The lower pait is thickl}- beset with frilled mouths, there being short, 

 isolated, gelatinous knobs strewn between the mouths and a short, rounded terminal knob 

 at the free end of each arm, about one-sixth as long as the arm itself. There is also a large 

 cluster of about 8 to 20 linear filaments upon the arm-disk at the bases of the 8 mouth-arms. 

 These are about 1.5 times as long as the diameter of the bell. 



Central stomach large and cruciform, 8 radial-canals arise from it and extend outward 

 to the marginal sense-organs; of these the 4 interradial canals are long and the 4 perradial 

 ones short. Between these 8 main canals are numerous, slender canals which arise from the 

 periphery of the stomach and anastomose with themselves and with the main radial-canals. 

 All of these canals are set into communication one with another by means of the circular 

 canal near the bell-margin. On its outer side the ring-canal gives off a network of slender 

 vessels which anastomose over the lappets. The subgenital porticus is very small. Color ( ?) 



Vanhoffen describes 3 examples of this medusa from Assab, on the Red Sea. They were 

 found in September. He gives it the generic name Desmostoma, defining the genus as being 

 similar to Mastigias, but with a large cluster of filaments upon the arm-disk between the 

 mouth-arms. The distinction appears to me to be too slight for generic, although important 

 for specific, differentiation. 



Mastigias (?) rosea Vanhoffen. 



Rhizostoma rosea, Reynaud, 1830, in Lesson's *'Centurie zoologique," p. 97, planche 34. 



Toxorlylus roseus, .Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, p. 153.^Haeckel, 1880, Syst. der Medusen, p. 586. — 



Lendenfeld, von, 1884, Proc. Linnean Soc. New Soutil Wales, vol. 9, p. 2S8. 

 Mastigias roseus, Vanhoffen, 1888, Bibliotheca Zoologica, Bd. i. Heft. 3, p. 45. 



Disk flat and hat-shaped, short, deep radial furrows on the exumbrella surface between 

 the lappets; 56 to 64 ( ?) small, elongate, marginal lappets, all of the same size and shape. 

 8 separate mouth-arms, hardly as long as the bell-radius; upper part of each arm cylindrical, 



