9OO OYSTERS, AND ALL ABOUT THEM. 



chances to have settled on the back of a lobster or a crab 



j 



he is obliged to join in the excursions of his unwitting 

 entertainer, whether he likes it or not. Fortunately for 

 both parties, these Crustacea cast their shells periodically, 

 or the oyster would become a confirmed rover, and when 

 he grew to any size his presence would most probably 

 become very unpleasant to the unlucky crab, who would 

 be unable to levy any tolls for his locomotive accommoda- 

 tion. 



In Frank Buckland's "Log-book of a Fisherman and 

 Zoologist," a picture is given of a terrapin that uncon- 

 sciously carried an oyster on the lower part of his back ? 

 close to the tail, till it had attained a very large size. 



From the above it will readily be surmised by the 

 reader that the future circumstances of a single brood of 

 the oyster are marked by a great and often strange diver 

 sity. Mr. Busk mentions (a] the valve of an oyster-shell 

 which resembles a combination between an oyster and a 

 pholas, one of the rock-boring molluscs. He thought 

 that the oyster had encased the pholas, or, at least, that 

 the pholas is enveloped in its valve. Professor Henslow, 

 however, has come to a different conclusion : 



" I suspect," he says, " that such is not the case, and 

 that Mr. Busk has the genuine shell (one valve) of an 

 oyster only. A specimen of a fossil oyster which I pre- 

 pared for the Ipswich Museum, a few weeks ago, seems to 

 explain Mr. Busk's puzzle. This shell (probably a detrital 

 relic from the Suffolk drift) had attached itself by the lower 

 convex valve to an ammonite, and as it grew, had taken in 

 a very complete manner the impression of its whorls. 

 But the curious result has been that the upper valve, which 

 (a) " Annals and Magazine of Natural History," March, 1855. 



