44 THE NAUTILUS. 



This meant a journey of from five to fifty yards and some of 

 them may have gone farther. After deep water is reached the 

 opercuhim is not drawn entirely over the foot but just suffici- 

 ently so to permit the gray, wrinkled flesh to protrude all around 

 the operculum and just level with the aperture of the shell. 

 This is the condition of hibernation for the winter. This was 

 evidenced by examination of all stations in February 1915 when 

 the dormant condition was found to be characteristic even for 

 the older and weaker individuals who had completely lost 

 their opercula. Some of the feebler individuals were unable to 

 reach the deeper water and stopped where the water always 

 runs in a swift current. Here, they bedded in pockets to the 

 number of several hundreds. A few were discovered in the 

 mud-flat channel where there is an inch of water at the lowest 

 tides but these always present the appearance of extreme old 

 age. 



Migration of Ilyanassa upstream began on either April 6th or 7th 

 and continued during the following two weeks, the more vigor- 

 ous of the migrants proceeding upstream in the interval between 

 April 8 and 15. Showers fell during the 5th and 6th which 

 warmed the water and reduced its density. Crawling steadily 

 they reached their summer habitat in four days. At this time 

 their distribution on low-tide flats was very characteristic. A 

 dozen snails picked up at random would include smaller, older 

 and more eroded individuals than would be the case if the lot had 

 come from the channel. Evidently, these snails were the last 

 to migrate in the fall. They were followed by a larger lot with 

 spires worn very little, opercula unbroken and with a more 

 brilliant cuticle. These spread out over the flats and inter- 

 mingled with the cripples already in possession. This differ- 

 ence in the general average w' as quite perceptible in the first 

 stages of the migration but was soon obliterated. An economic 

 distribution of the species is probably never accomplished and 

 adjustment is probably not attained before the summer. Even 

 in summer Ilyanassa roves about a great deal on the mud flats 

 and they may always be found in the channels in small num- 

 bers. 



The migrating Ilyanassa are very interesting to watch. At 



