MEDUSA. 147 



This little JEquorea differs from the other species of the genus in the small numbers 

 of its tentacles, and in the shape and position of the gonads upon the radial canals. 



Mesonema, Eschscholtz, 1829 ; ex Browne, 1904. 



^Equoriidse with numerous simple, unbranched radial canals. Stomach circular, with 

 lower wall quite rudimentary. Mouth nearly as large as the diameter of the 

 stomach and cannot be closed. 



Mesonema pensile (Modeer), 1791 Plate II., figs. 11 to 15. 



Medusa sp., Forskal (1776, p. 9, tab. xxviii. B.). 

 Mesonema ccelem pensile, Modeer (1791, p. 32). 

 Mesonema pensile, Haeckel (1879); Browne (1904, p. 733, pi. lv., fig. 4; pi. Ivii., figs. 2-9). 



In my Report upon the Hydromedusae of the Maldive Islands I gave a description 

 of Mesonema pensile (Modeer). In this Ceylon collection there are fragments of a 

 specimen which I believe belongs to this species. The specimen is from the Cheval 

 Paar, Gulf of Manaar, and is broken up into about twenty-five pieces, which together 

 represent only a portion of the whole medusa. Fortunately some of the fragments 

 contain all the organs of the medusa, and it is possible, within certain limits, to give a 

 description and to identify the species. 



This medusa is so peculiarly constructed that all the organs lie close to the margin 

 of the umbrella. The umbrella is rather like a plano-convex lens in shape and of 

 great thickness. Around its periphery lie the mouth, stomach, radial canals, marginal 

 tentacles, and sense-organs. These organs are all close together, the distance from 

 the oral lips to the margin of the umbrella is only about 20 millims. To judge from 

 the curvatures of the stomach and the margin of the umbrella on the three largest 

 fragments (the largest fragment which contained all the organs measures 35 millims. 

 in length), the diameter of the umbrella should be much larger than that of the 

 largest Maldive specimen, which measured about 60 millims. in diameter. I think 

 that this medusa when alive was probably about twice the size of the largest Maldive 

 specimen. 



The stomach (fig. 14) is rudimentary, and its lower wall is about 4 millims. in 

 length. The margin of the mouth is furnished with a large number of long narrow 

 lips, which are strengthened by an external rib. The length of the longest lips is 

 about 4 millims. Among the lips there are many small ones in the course of 

 development. In structure and shape the oral lips are exactly like those of the 

 Maldive Mesonema, but they are a little longer. The lower wall of the stomach is 

 also longer, twice the length. 



The radial canals are very numerous, and very short ; the distance from margin of 

 the stomach to the circular canal is about 9 millims. The radial canals usually run 

 straight from the stomach to the circular canal, and in one fragment the canal 

 system is quite normal, but some fragments show that the short portion of the canals, 



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