224 J. M. D. OLMSTED 



also due to Mr. W. F. Clapp for the identification of the majority 

 of the mollusks referred to in this paper. 



1. The huge slug, Veronicella schivelyoe Pilsb., which, ac- 

 cording to Verrill ('02), is not known to occur elsewhere than in 

 Bermuda, shows direct monotaxic locomotion, i.e., the pedal 

 waves pass from posterior to anterior and extend the full width 

 of the foot. In Veronicella, when the animal is moving, there 

 are always about eleven such waves, a condition which is in 

 strong contrast to another pulmonate abundant in Bermuda, 

 Onchidium floridanum, which shows the same type of locomotion, 

 but shows only one or two waves at a given time. The number 

 is fairly constant for individuals of Veronicella having very 

 different lengths. It may even be that the number is constant 

 for the species and that the difficulty of counting the rapidly 

 moving waves in the small animals is responsible for the small 

 differences obtained. 



These animals give an interesting reaction if they are dis- 

 turbed after having once come to rest. When one taps the animal 

 lightly, as for instance with a pencil, at any point on the posterior 

 third of its dorsal surface, waves appear on the foot varying in 

 number from the whole eleven in the case of a light tap, to five 

 after a strong tap. In the former case the slug usually continues 

 producing pedal waves and moves away, while in the latter, the 

 most posterior waves are the most pronounced, and as they pass 

 anteriorly they diminish in intensity, and all disappear after two 

 or three new waves have been added to the original number. If, 

 however, one taps the slug's head, this part is pulled back and 

 no waves at all appear on the foot. When the animal is moving, 



