262 bulletin: museum of comparative zoology. 



marginal papillae, near the outer edges. These papillae are large ami 

 prominent, but extend only slightly, if at all, beyond the margin of the bell. 

 The otocyst itself, containing a number of minute spherical otoliths, is covered 

 over by a curtain-like structure (Plate 6, Fig. 23). 



The tentacles, borne on the exumbrella, .some distance from the bell 

 margin, are short, very numerous, about five hundred in number, and alter- 

 nate with as many small dorsal lappets. There are about forty-eight 

 chymiferous tubes in the region of the stomach, l)Ut they branch frequently, 

 and occasionally anastomose, so that at the bell margin there are about one 

 hundred and seventy to one hundred and seventy-five. The eight canals 

 running to the sense organs do not branch, nor do the eight which run to 

 the middle of the marginal lappets. The mouth arms are long and broad, 

 fringed with innumerable minute tentacles, and in life they hang slightly 

 below the bell opening, but do not extend outward beyond its margin. The 

 structure of the mouth parts, and their complexity, separates this Medusa from 

 every other member of the genus. The mouth itself is a simple cruciform 

 opening, but it is surrounded by elongated lips, which hang far below the 

 bell opening, suggesting in appearance a small or immature Cyanea. These 

 lips, which are undivided, and form an extremely sensitive and mobile 

 curtain completely .surrounding the mouth, are thrown into four main folds, 

 rendering them cruciform in cross-section, and alternating in position with the 

 gonads. They bear in addition numerous complex lesser folds, increasing in 

 number toward the free margins. The living Medusa constantly contracts and 

 expands the mouth parts with every motion of the bell, and a photograph 

 taken at the time shows them much further extended than I have figured 

 them. The four gonads are of the horseshoe form typical of Aurelia, and are 

 rather small. But owing to their bright color they are very conspicuous. The 

 subgenital pits are widely opened. 



This Medusa is extremely brilliant and striking in the water. The entire 

 bell is of a delicate lilac tinge ; the canals and tentacles are pinkish violet, 

 and the gonads, and in mature specimens the edges of the mouth arms and 

 lips are bright violet. The color varies much, — some specimens showing more 

 pink, others more violet or blue. 



Abundant on the surface on several occasions. We found it first on January 

 1, off the east face of Suvadiva atoll, and inside the atoll, when it was so 

 abundant that it filled regular lanes in the water, and the tow brought in 

 nothing else. After that we found it in nearly every other atoll. 



Aurelia nialdivensis bears little resemblance in appearance to any other 

 Aurelia, and this is especially important in a genus where all the other species 

 are extremely closely allied. The most striking feature of this Medusa is, of 

 course, the great development of the mouth jiarts, which, as I have noted, 

 suggest in their structure the young of Cyanea ; but the arrangement of the 

 chymiferous tubes and the structure of the sense organs are also both 

 distinctive. 



