146 OYSTERS, AND ALL ABOUT THEM. 



high and low ; and the striated appearance of the top or 

 outer covering is produced by the edges of the higher 

 plates. This appendage is capable of receiving a high 

 degree of polish, and in that state resembles ivory and is 

 equally close-grained. In the fry the orifice is larger in 

 proportion to that of the adult, and is placed on one side. 

 The beak of young Specimens is sometimes much produced,, 

 and at other times slightly incurved. When the shell is 

 thin, the long muscular scar seen through the upper valve 

 resembles a white line. The varied and nacreous hues of 

 the shell rival in lustre those of the opal. 



A group of these specimens from Lulworth Cove, on 

 a valve of Pecten opercularis, now before me, are of different 

 colours, white, yellow, and pink, and reflect their pearly 

 gleams in every direction. In substance the shell bears 

 some affinity to talc. Specimens from Bantry Bay, Lough 

 Strangford, and Exmouth roads, are larger than usual. 

 One from the first-named locality measures four inches in 

 diameter. Now and then, but rarely, the upper valve is 

 flat, and the lower or perforated valve is convex ; and in 

 one case the front half of the shell is divided into two 

 distinct lobes, owing to the continual obstruction and irri- 

 tation caused by a small branch of Sertularia abteh'na, 

 which had insinuated itself and grown up in front of the 

 Anomia. 



But a more curious instance of an adaptation to cir- 

 cumstances is presented by specimens which I found many 

 years ago on a mussel-bed in Swansea Bay, laid bare by an 

 unusually low tide. The orifice in every specimen was 

 completely closed by a series of thin vaulted plates, of the 

 same material as the shell. All the specimens were living, 

 and attached to the mussels by the byssal threads of the 



