Medusce of the Philippines and of Torres Straits. 187 



The 8 mouth-arms resemble those of . tuberculata, but there are window- 

 like openings in the lateral membranes, as in Lobonema smithii. The total 

 length of each arm is 81 mm., the upper arm being one-fourth as long as the 

 lower arm. At their widest part the arms are about three-fourths as wide as 

 they are long. The center of the arm disk is thickly covered with slender 

 filamentous appendages which terminate in nematocyst-bearing, swollen, 

 knob-like ends, as do the appendages of the mouth-arms of C. tuberculata. In 

 this Philippine Island medusa the appendages of the outer parts of the mouth- 

 arms are much less numerous and smaller than in C. tuberculata, but are similar 

 in general form to those of the Mediterranean medusa. The longest are about 

 15 to 20 mm. long. 



The cruciform central stomach gives rise t6 about 140 radial-canals, the 

 8 rhopalar canals being about twice as wide as the others, instead of being of 

 the same calibre, as in C. tuberculata. All these canals anastomose in a 

 network under the zone of the circular muscles. There is no distinct ring- 

 canal. In formalin the specimen is dull uniform yellowish-brown. 



It differs from Cotylorhiza tuberculata in having no radial-muscles, and in the 

 circular muscles being interrupted in the 8 principal radii. The subgenital 

 ostia and arm-disk are larger and the appendages of the mouth-arms smaller 

 and fewer than in C. tuberculata. Moreover, the peculiar window-like open- 

 ings in its mouth-arm membranes at once distinguish this species. 



These distinctions are indeed of such a nature that if one felt so inclined a 

 new genus could be established to receive this medusa. I believe, however, 

 that its relationships will be more clearly indicated by placing it in the genus 

 Cotylorhiza, within which it forms a well-marked species. 



Genus CATOSTYLUS L. Agassiz, 1862. 



Catostylus (in part), AGASSIZ, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 152, 153. 



GENERIC CHARACTERS. 



Rhizostomata triptera, in which the mouth-arms bear neither clubs, filaments, 

 nor other appendages. 16 radial-canals, 8 rhopalar, and 8 adradial. The 

 rhopalar-canals extend to the bell-margin, but the adradial-canals end in the 

 ring-canal. On both its inner and outer sides the ring-canal gives off anasto- 

 mosing vessels which may join with the radial-canals, but which do not connect 

 directly with the central stomach. Among characters of minor importance, 

 the marginal zone of circular muscles in the subumbrella is only partially 

 interrupted in the 8 principal radii. There is an exumbrella pit with radiating 

 furrows above each sense-organ. 



Catostylus purpurus Mayer. 



Catostylus purpurus, MAYER, 1910, Medusse of the World, vol. 3, p. 671, fig. 412. LIGHT, 1914, 

 Philippine Journ. of Science, vol. 9, p. 207. 



This form is closely related to Catostylus stiphropterus, from Ternate, but 

 differs in the number and arrangement of its marginal lappets, and in its deep, 

 uniform purple-brown color. Light (1914) describes this medusa from life, 

 whereas Mayer had only preserved material. In life the bell is higher than a 

 hemisphere, whereas in its contracted state in preservative fluids it is flatter 

 than a hemisphere. When mature it is deep purplish brown, and the sense- 

 organs have brilliant silver ocellus-like spots which are larger in small than 

 in full-grown medusae. When young the medusa may be plum-colored, or even 

 translucent white. Small cyclops-like Crustacea were found by Light to be 

 commensal with this medusa, the crustaceans lying upon the rhopalar canals 

 close to the sense-organs. 



