268 ME. A. B. HUNT ON THE INFLTJENOE OE 



rest, appear at first sight to be a source of danger in case it were 

 overturned. They are in reality self-acting pieces of mechanism 

 that will, in the majority of instances, ensure the moUusk being 

 ultimately left in its normal posture should it encounter wave- 

 currents sufficiently strong to upset it. On examining a speci- 

 men of AporrJiais pes-pelecani it will be seen that, when on its 

 back, it lies indifferently on either side of a line drawn between 

 two points, of which the end of the middle wing-like process is 

 one, and one of the nodules on the body-whorl the other. The 

 shell will rock freely backwards and forwards across this line ; and 

 experiment proves that a very moderate alternate current will 

 suffice to replace the shell in its normal position. I have tried 

 this experiment over and over again, not only with AporrJiais, but 

 also with heavy foreign shells furnished with spines, processes, 

 and more or less developed lips, such as Murex, Fteroceras, and 

 Strombus. In many cases the righting-action of wave-currents is 

 most marked. 



With Aporrhais, on the same exposed areas, are often found 

 the Gastropods Nalica catena, JBuccinum undatum, Nassa reticu- 

 lata, Bulla hydatis, and PMline aperta. All these are manifestly 

 unsuited to withstand wave-currents on the surface of the bottom ; 

 but there is no occasion for making the attempt, as all burrow 

 freely, travelling through the sand beneath the surface. 



Asierias aurantiaca and. Antedon rosaceus are good examples of 

 two Echinoderms that successfully encounter wave-currents by 

 methods totally diverse. The Asterias lies on the sand with an 

 extended and rigid base, where its flattened form is eminently 

 calculated to offer slight resistance to wave-currents. But as 

 though this were insufficient for its safety, it has the power of 

 sinking vertically in the sand, and of thus securing itself from all 

 danger. Antedon rosaceus (the feather-star) is found frequent- 

 ing the clear water off rocky headlands, where it is necessarily 

 exposed to strong currents, both tidal and wave-engendered. 

 Here nothing will avail but sheer strength in holding on ; and 

 this the feather-star possesses in an eminent degree, from the 

 time it is first attached to weed or zoophyte in its early stages of 

 growth, to the time when, a full-grown adult, it is free to exer- 

 cise its limited powers of locomotion. I may here refer to 

 Mr. Osier's description of the Spataoigus sinking vertically into 

 the sand by the action of its short, fiat bristles (Phil. Trans. 1826, 

 p. 347). 



