AUTHOR S ABSTRACT OF THIS PAPER ISSUED BY 

 THE BIBLIOGRAPHIC SERVICE, SEPTEMBER 28, 1917. 



NOTES ON THE LOCOMOTION OF CERTAIN 

 BERMUDIAN MOLLUSKS 1 



J. M. D. OLMSTED 



ONE FIGURE 



Vies ('07) has classified the types of gastropod locomotion 

 according to the region of origin and method of progression of the 

 pedal waves. He applies the term direct to those waves which 

 pass over the foot in the direction in which the animal itself is 

 moving, i.e., from posterior to anterior, and retrograde to those 

 which proceed in the opposite direction. He has made a further 

 subdivision with reference to the lateral extent of waves, calling 

 the locomotion monotaxic when each wave extends across the 

 whole width of the foot, di- and tetrataxic when two and four 

 parallel systems, respectively, are exhibited on a foot. Parker 

 ('11) found that it was possible to distinguish two subtypes in 

 ditaxic locomotion, one in which the waves of the two sides 

 alternated in position, and the other in which they were opposite 

 to each other. Parker also made a further addition to the types 

 of gastropod locomotion when he described the "arhythmic 

 pedal movements" of Illyanassa obsoleta Say. 



In the present paper further examples of several of these types 

 are reported, as well as several new types, which present decided 

 peculiarities A method of demonstrating that pedal waves 

 are concavities is given, and backward locomotion is described. 

 The work was done at the Bermuda Biological Station in the 

 summer of 1916. I am indebted to Dr. G. H. Parker for sug- 

 gesting a study of gastropod locomotion, to Dr. W. J. Crozier 

 for his courtesy in turning over material to me, and to Dr. E. L. 

 Mark and to the Trustees of the Humboldt Fund for having 

 made it possible for me to go to Bermuda. My thanks are 



'Contributions from the Bermuda Biological Station for Research. No. 73. 



223 



