NOTES ON COMMON SPECIES OF TKOCHUS. 461 



seaweed. The jaws in the species of Trochus mentioned are 

 not strong enough to be useful in these directions. They 

 probably protect and give firmness to the upper lip, leaviug 

 the work of drawing in food particles to the odontophore 

 and the lip papilla. 



Randies states that there is close agreement in anatomical 

 characters between the various species of Trochus studied by 

 him, and this agreement is very marked in the two species 

 already named. Still, there remain differences between 

 T. crass us, Mont., and T. obliquatus, Gmel., which it 

 seems possible to correlate with the differences in their habits. 

 This must not be taken to imply, however, any belief that 

 the two species are specially related to one another, we have 

 no evidence at present on this point. 



T. obliquatus, Gmel., occurs in abundance where there is 

 a reasonable amount of plant life and adherent growth on 

 rocks washed by the tide, and it frequents both the upper 

 and the under sides of boulders, often retiring beneath when 

 it is exposed to strong tide wash, or to heat, strong light, or 

 possibilities of drought when the tide is away. It crawls 

 over and browses on a great variety of Algee, but has hitherto 

 been classed too exclusively as a vegetable feeder. It is 

 almost omnivorous, and in early summer may often be found 

 attacking the egg-fringes and chains of Nudibranchs and 

 other forms. Remains of eggs and other auinial matter are 

 frequently seen in sections of the gut. 



T. crassus, Mont., is found, to some extent, with the pre- 

 vious species, but it lives, for the most part, nearer high-tide 

 level, so much so that specimens may remain for a considerable 

 time in corners washed only by high spring-tides. It crawls 

 over the rocks chiefly above half-tide level, but is more 

 lethargic than T. obliquatus, and less inclined to browse 

 on the larger Alg£e. Duiing stormy periods, especially in 

 winter, numbers may be found huddled in sheltered nooks, 

 often with a number ofLittorina littoreaas companions. 



As is well known, the spire of T. obliquatus is typically 

 much lower than that of T. crassus, and this is probably 



