00 THE NAUTILUS. 



surface it looks, as has been stated, as though the animal was pro- 

 gressing by steps. This appearance is very striking when the animal 

 is viewed from in front, but when viewed from the rear the regular 

 alternation of the apparent steps strongly recalls the movement of an 

 elephant, as noted above. In either position, the lifting of the edge 

 of the foot as the wave passes off, gives the animal the appearance of 

 advancing by leisurely strides. 



Tudora armata (C. B. Ad.). In this species the wave movement 

 is similar to that in G. bronnii, but it is somewhat more rapid, and 

 the waves follow each other at a shorter interval; nevertheless the 

 forward movement of the shell is slower on account of the shorter 

 wave, being about 50-60 mm. per minute. The foot, when the ani- 

 mal is moving, is about 8 mm. long by 3 to 4 mm. wide; the surface 

 of contact is about 1 mm. on each edge of the foot, with an inter- 

 space of seme 1 ram. between the two sides of the foot when actively 

 moving. The passage of the wave the entire length of tlie foot re- 

 quires about 5 seconds; the alternate waves follow each other every 

 4 seconds, so that the two waves can generally be seen simultaneously 

 if the moving animal is examined from the underside. Seen in this 

 way the two waves of contraction are about 5 mm. apjirt, and the 

 form of the foot resembles a swelled barleycorn. In crawling, the 

 shell is balanced on the middle of the operculum, and the swaying 

 gait is even more noticeable than in tlip last, from the pro[)ortionately' 

 greater length of tlie shell, which in this species measures: length, 

 1;") mm.; width, 8 mm. Of course in all cases the first half of the last 

 whorl rests on the operculum. The foot of this species is of a slaty- 

 gray color, the tentacles and rostrum darkei", and the eyes black. 



Aihimsiella irrorata Gloyne, Figures 1 and 2. This species is 

 quickei" in its niovenients than either of the others examined, but the 

 actual distance traversed in unit time is less than in C. bronnii or T. 

 ormaUu The wave motion is rapid; the wave of contraction traverses 

 liie entire length of the foot from back to front in 2 seconds, and the 

 waves follow each other every 3 seconds on each side, or there are 40 

 wav"s per minute, 20 on each side. The distance traversed in tliis 

 time is about 50 mm. Tlie shells vaiy in size, but the foot is about 

 7 n)m. long when the animal is in motion; its width is about 3-4 mm. 

 As is the case with the other species, the shell is normally carried bal- 

 anced on the o[)erculum, the round of ihe penultimate wliorl resting 

 in the hollow of the rather small, circular operculum. As this is so 



