70 



Transactions. 



Although in the original thesis submitted to the University of New 

 Zealand the histological structure of the various organs was discussed and 

 illustrated, I have thought it advisable to omit these matters in the present 

 paper. 



I wish here to express my indebtedness to Professor Benham for his 

 valuable suggestions and great help in preparing this paper for publication. 



Habits. 



Am-phihola crenata is a basommatophorous pulnionate gasteropod found 

 living on mud-flats in sheltered bays, both in brackish and in salt water. 

 It belongs to a series of pulmonates sometimes termed " gehydrophilous " 

 (Cook, 1895, p. 18), in which, while the gill has been replaced by a '' lung," 

 the animal has not become truly an inhabitant of fresh water. Amphibola 

 and some other genera, such as Gadinia and Siphonaria, are '' intermediate 

 between essentially fresh-water and essentially marine species." 



The larger specimens of Amphibola are found cjuite close to the sea, 

 the smaller ones farther up the mud-flat. They occur in enormous num- 

 bers on all the flats around the Otago Harbour, and, indeed, all along the 

 coast of New Zealand. They are, of course, covered during high tide, but 

 are exposed to view at low tide, so that the greater part of their life is 

 passed out of water. Nevertheless, sufficient water is retained in the 

 mantle-chamber to keep the tissues moist. 



These animals are exceedingly sluggish. When they are in their natural 

 surroundings one has to watch them very closely to see whether they are 

 moving or not ; but if they are placed in a little sea- water in a dish their 

 method of locomotion is readily studied. When examined on the shore the 



only evidences of movement are the slow 

 twirling of the shell as it is being drawn 

 up to cover the slightly extended head 

 and foot, the latter of which is concealed 

 in the mud, and the furrow traced out 

 on its path. The most striking feature 

 of this movement is the very small part 

 of the foot that is exposed at any one 

 time. Its method of locomotion is as 

 follows : A small portion of the anterior 

 part of the foot is protruded, and this 

 acts as a temporary anchor. The shell 

 is then drawn up to cover the exposed 

 part, and as it is twisted from left to 

 right during the process it leaves a small 

 part of the foot exposed on the left side 

 and behind. The animal then glides 

 slowlv forward for a space without 



Fig. 1. — AmjjhiOola crenata from 

 below (natural size), as seen 

 creeping up the side of a glass 

 vessel of fresh water and thus 

 exposing the whole of the foot. 

 The two lappets of the heatl pro- 

 ject only slightly in front of it. 

 /, foot ; h, head ; m, mouth ; 

 s, shell. 



a space 



twisting the shell at all. The above process is repeated, the movement 

 of the shell sometimes being from right to left . The shell is carried at an 

 angle to the surface on which the animal is walking, the right side of the 

 shell being raised a little from the mud, while the left side almost touches it. 

 The animal is very sensitive, retracting into the shell at the slightest touch 

 or at any disturbance of the water. 



Although air-breathing, Amphibola is able to live a considerable time 

 immersed in water, either fresh or salt. If kej)t in a glass of fresh water 

 the cover of wliich is sealed up it will live for a week ; if completely 



