360 Mr. N. Colgan on LocomoUon and the 



often found swarming in its juvenile state in the littoral zone 

 of the Dublin coast, is the only Pelecypod whose habits of 

 locomotion I have observed, A number of young individuals 

 collected at Bullock on the 21st April last, and averaging ^ 

 inch in the longer diameter of the shell, were found to be 

 expert climbers. Their method of climbing to the water 

 surface, though in principle no doubt the same as that 

 employed by the Gastropods, was utterly different in appear- 

 ance. Instead of mounting the tube with an even gliding 

 motion whose phases eluded observation, the young Modio- 

 larias hoisted themselves by intermittent and violent muscular 

 cojitractions o£ an inordinately long foot, whose tip was 

 anchored in advance of the animal, no doubt by a stiff mucus, 

 as a preliminary to each upward lift of the animal and its 

 shell. Watched with a hand-glass this operation conveyed a 

 grotesque suggestion of a sailor climbing a rope hand-over- 

 hand. 



When halfway to the water surface one of the individuals, 

 having withdrawn its foot completely into its shell, was seen, 

 notwithstanding, to maintain its position on the side of the 

 tube. A close scrutiny showed that the animal was fixed by 

 a single delicate byssus thread neatly soldered to the glass by 

 a terminal expansion. Before long I had the pleasure of 

 watching the operation of byssus-making going on. The 

 animal's foot was protruded to full length beyond the anterior 

 end of the shell near to where the byssus-thread was fixed. 

 For some seconds the foot was worked to and fro over the 

 glass and then quickly withdrawn, when a second byssus- 

 thread was seen to be fixed in position. After an interval of 

 about a minute the foot was again shot out to full length, 

 this time from the posterior end of the shell. Then for nearly 

 half a minute the tip of the foot kept working over the side 

 of the tube in a nervous, hasty, irresolute fashion, fumbling, 

 in fact, and when it was at length withdrawn left three 

 radiating byssus-threads fixed by their knobbed extremities 

 to the glass. 



In addition to the power of spinning a byssus, which it 

 possesses in common with all the Mytilida?, Modiolaria discors 

 can produce a suspensory slime-thread and employ it in 

 climbing. On the 24:th April last one of many specimens 

 left floating on the water surface in a tube was found to have 

 lowered itself by a slime-thread to a depth of | inch. When 

 watched this individual was seen to climb slowly up its 

 thread by applying to it the tip of its long foot, the whole 

 ascent being made iu four minutes. 



