226 J. M. D. OLMSTED 



animal is moving. During locomotion, a wave starts next this 

 middle line, and is followed by another near the outer edge of the 

 foot. Then a wave appears on the other side of the median 

 line, and in turn is followed by a wave near the outer edge of that 

 side. If one considers the foot as divided into quarters by lines 

 running parallel to the long axis of the foot, and if he numbers 

 these quarters from left to right 1, 2, 3, 4, then the waves appear 

 in this order, 2, 1, 3, 4 or 3, 4, 2, 1. 



8. Columbella mercatoria L. is also retrograde tetrataxic in 

 its locomotion. 



9. Cypraea exanthema L. exhibits a type of locomotion differ- 

 ent from any described by Vies ('07) or Parker ('11). Only one 

 specimen was brought to the laboratory during the season and 

 the following description is taken from this animal. During 

 the first three or four days in the laboratory it moved constantly 

 in its jar, coming to rest always on a lateral wall. Later, lo- 

 comotion occurred only when it was disturbed. 



The foot was somewhat pointed at the anterior end being 

 more rounded at the posterior. The lateral edges were practically 

 parallel. In repose the length of the foot was 8.5 cm. and the 

 width at the anterior end 6, but when moving the foot was 

 lengthened to about 9.5 and narrowed to 4 cm. At the extreme 

 anterior edge of the foot (fig. 1) was a narrow (0.5 mm.) band of 

 light, almost white tissue, which exhibited a constant rippling 

 motion. This seemed to bear no relation to the ordinary waves 

 appearing on other portions of the foot. 2 I made many attempts 

 to cause the animal to attach itself to a glass plate by some 

 region of its foot other than the extreme anterior part, but in 

 no case was I successful. For the act of attaching, it seemed 

 necessary that the anterior part of the foot, including the white 

 band, be in contact with the substrate, but when the whole foot 

 once became attached I could, by a quick shove, push the an- 

 terior three-fourths off the plate, and still the animal was able to 

 cling perfectly with the remaining fourth of its foot. When in 

 this position, it would bend the anterior edge of the foot around 

 and attach it to the other side of the plate, so that its foot was 



2 Cf. Parker's ('11) description of the locomotion of Illyanassa obsoleta. 



