692 



MEDUSAE OF THE WORLD. 



The only difference between this genus and the closely allied Lorifera is that the frilled 

 mouths are developed even to the tips oi the lower ends ot the mouth-arm and there is no 

 terminal club, whereas Lorifera has a naked terminal club. 



Thysanostoma thysanura Haeckel. 



( ?) Rhizoitoma brachyura, LESSON, R. P., 1829, Voyage de la Coquille, Zoophyt., tome 2, p. 153; 1830, Centurie Zoologique, 

 p. 227, plarche 80. 



Th \>anostowti lh\<nnitra, HAECKEI,, iSSo, Syst. dcr Medusen, p. 625, taf. 39, fign. 1-9. SCHULTZE, L. S., 1898, Denkschr. 

 Med. Nat. GcsclL, Jena., Bd. 8, p. 448, taf. 33, fig. 3; taf. 34, fig. 8. MAAS, 1903, Scyphomedusen der Siboga Expedition, 

 Monog. ll, p. 75, taf. lo, fign. 93, 94; 1906, Revue Suisse de Zool., tome 14, p. 105. KISHINOUYE, 1910, Journal Col- 

 lege of Sci., University of Tokyo, vol. 27, art. 9, p. 23. 



Thvsanostoma denscrisfum, KISHINOUYE, 1891;, Zoological Magazine, Tokyo, vol. 7, No. 83, p. 133, plate 18, figs. 1-13. 



The bell is 90 to 120 mm. wide. The exumbrella exhibits polygonal facets or granular 

 elevations which are larger at the center than at the margin. Its outline is dome-like and 

 flatter than a hemisphere, recalling the appearance of a shield. There are 8 marginal sense- 



FIG. 420. Th\sanostotna thysanura. Drawn by the author, from a specimen taken in a 

 seine by the U. S. Fisheries Bureau steamer Albatross at Panabutan Bay, Philip- 

 pine Islands, Feb. 6, 1908. 



A, oral view showing all but one of the mouth-arms cut off. One mouth-arm is cut off 

 close to its point of origin, but the other 6 are cut off at their widest, Y-shaped 

 regions. B, side view of basal part of mouth-arm, with section of same. C, sec- 

 tion near distal end of mouth-arm, somewhat enlarged, showing T-shape of cross- 

 section of arm the and 4 arm-canals. D and E, rhopalar lappets from subum- 

 brella and exumbrella sides respectively. 



organs which are flanked by 16 small, pointed lappets and between each successive pair of 

 sense-organs are 6 to 12 bluntly rhomboidal lappets which are very variable in size even in 

 different parts of the same octant. The sense-clubs have a pigmented mass of lithocysts 

 and there is a very small, shallow, simple, exumbrella pit. 



The 8 mouth-arms are each about 1.5 to 3 times as long as the bell-diameter; upper arm 

 only about one-twelfth as long as the lower arm. Lower arm delicately formed, j-winged 

 and Y-shaped or T-shaped in cross-section throughout its length; in its upper part it tapers 



