NOTES ON COMMON SPECIES OF TROCHUS. 469 



by various channels from the roof of the branchial cavity 

 goes back along the efferent ctenidial channel to the left 

 anricle, which also receives important supplies from the left 

 kidney. The left kidney thus gets its blood from the 

 efferent channel of the right kidney, and passes it on to the 

 left anricle, but its blood spaces are intimately associated 

 with those of the neighbouring part of the roof of the 

 branchial cavity, so perhaps a good deal of what it con- 

 tributes to the left auricle has been aerated. 



As the efferent channel from the right kidney communi- 

 cates with the right auricle before reaching the left kidney, 

 past which blood flows to the left auricle, it follows that 

 right and left auricles are not so very indirectly connected 

 with one another. This is another point of resemblance 

 between Trochus and Haliotis. 



Reference has been made to the possible respiratory 

 activity of the roof of the branchial cavity, especially in 

 T. crassus, Mont., and it is interesting to notice that the 

 corresponding tissue seems to have acquired respiratory 

 functions in Patella, which is also often a mid- to high-tide 

 form. 



In a recent paper Spillman (11) incidentally mentions the 

 course of the circulation, but the vagueness of the state- 

 ments made renders a discussion of his views unnecessary. 

 He has evidently not given any special attention to this 

 particular subject. 



Bionomical Notes. — T. crassus, Mont., is often found 

 in fairly large numbers huddled together in protected gullies 

 and corners during the winter, especially when the weather 

 is stormy. In summer it is interesting to watch these 

 animals, often following one another's tracks as if the fresh 

 trail of mucus were a help in progression. They also have 

 the habit of mounting on one another's shells, where they 

 apparently browse the small Algae, etc., on the surface. As 

 Trochus has no mating habits (in common species, at any rate), 

 these peculiarities in behaviour may be thought of as the 

 indistinct beginnings of that mutual recognition, perhaps 



VOL. 51, PART 3. — NEW SERIKS. 35 



