86 THE NAUTILUS. 



possess this type of movement. The method of progression of Ad- 

 amsiella irrorata Gloyne, Goloibostylus bronnii (C. B. Ad.) and 

 Tudora armata (C. B. Ad.) has been carefully studied from speci- 

 mens obtained in Jamaica during the past summer (1910), and an 

 account of their movements will apply in general to all of the above 

 species. 1 



Unlike most snails, the entire under surface of the foot is not 

 applied to the surface upon which they move, but they walk on the 

 edyes of the foot only. The foot, when retracted into the shell, folds 

 down the median line of the under surface; and, when protruded for 

 walking, this same form is retained, so that ordinarily only the two 

 outer surfaces are involved. A wave of contraction, lifting a portion 

 of this edge of the foot, proceeds from the posterior to the anterior, 

 the wave moving forward alternately on the two margins of the foot, 

 and with its advance, first on the right side and then on the left, 

 producing a swaying gait that is characteristic of the movement of 

 all the land operculates above enumerated. The wave movement is 

 quite independent in the two sides of the foot, and this is easily seen 

 when the animal is examined from the under side, when crawling 

 over a surface of glass. As the wave passes off at the anterior end 

 of the foot on one side the succeeding wave begins at the posterior 

 end on the other side, and thus the animal acquires the waddling or 

 swaying gait characteristic of this type of movement. As the wave 

 passes off anteriorly a part of the foot is lifted and moved forward; 

 as the wave appears at the posterior end a part of the foot is lifted 

 and moved forward also, so that seen from the front or rear espe- 

 cially, the animal seems to be walking upon stumpy legs, and the 

 movement recalls that of an elephant as seen from the rear. The 

 trail made, when moving over dry surfaces (as the animals normally 

 have to when in their native habitat), is double, only the edges of 

 the foot being involved, and this double trail may always be seen 

 when these snails are actively moving about. The details of the 

 movement in the three species that were especially examined is given 

 below. 



Colobostylus bronnii (C. B. Ad.), Figure 3. This species is larger 



1 In a recent paper on the mollusca of Mandeville, Jamaica, by Pilsbry and 

 Brown this mode of progression is briefly described as it was observed in 

 Colobostylus jayanus rufilabris (C. B. Ad.) and in Tudora armata (C. B. Ad.). 

 See Proc. Acad. Nat. Sci., Sept., 1910, p. 52^. 



