12 THE CRASPEDOTE MEDUSA OLINDIAS AND SOME OF ITS NATURAL ALLIES. 



II. GONIONEMA DEPRESSUM sp. nov. 



This is a pretty species common among the eel-grass growing within the wharves 

 of Yokohama, and specimens can easily be obtained at any hour of the day by towing 

 in such situations by means of a weighted net. I have never seen the medusa on 

 the surface of the water during the daytime. The Woods Hole species, for which 

 Mayer has recently proposed the name of G. murbachii, is stated to come to the sur- 

 face at night, and the towing for the medusa appears to be performed there only in 

 the evening; but it is probable that the animal never quits the eel-grass entirely, 

 since it is known that the grass grows rank in the eel-pond, where it is always hunted 

 for. The Yokohama species has a rather shallow open umbrella, which may measure 

 20 millimetres by 8 millimetres or a little more. The smaller examples have the 

 umbrella relatively deeper; one of 4 millimetres in diameter measures just as much in 

 height. The jelly is only moderately thick. The swimming movements are vigorous, 

 but only a few pulsations are made consecutively at a time, after which the animal 

 slowly sinks with expanded umbrella and outstretched tentacles until it touches some 

 object, when it attaches itself to it by means of the adhesive disks of the tentacles. 

 The manubrium is quadrate with distinct lips, and hangs down close to the level of 

 the umbrella margin. The radial canals are four, and the gonads are developed on 

 their lower walls along nearly their entire lengths, leaving only a small proximal and 

 an equally small distal portion free. In very young examples the gonads are simple 

 thickenings of the wall of the radial canals, but in larger ones they are thrown into 

 folds which are arranged alternately on either side of the canal. These folds remain, 

 however, very simple, and, so far as I have observed, are never divided into lobes 

 (PL II, Fig. 13). 



The tentacles are numerous; in an example of 18 millimetres in diameter there 

 were 59, and in another of 4 millimetres there were 32; 64 was the largest number 

 of the tentacles I have observed so far. They are very flexible, but are not as con- 

 tractile as the velar tentacles of Olindioides; they are armed with incomplete ring- 

 like warts, in which the nettle-cells are found. The most characteristic feature 

 of the tentacles, however, is that they bear at some distance from the tip each an 

 adhesive disk, by which the animal can securely attach itself to any external object. 

 When the tentacles are expanded, these disks are nearly flat and elliptical, but in 

 contracted tentacles they are more or less saucer-shaped, and are compressed along 

 the length of the tentacle (PL II, Fig. 11; PL III, Fig. 21). They consist of tall 



