BRITISH OYSTERS I OLD AND NEW. I9I 
east, show incipient costal ridges which I have not noticed in 
western shells. The ” plaits ” or shoots shown on the under 
valve increase yearly, and are fairly regular up to five years 
of age, when they have a tendency to become irregular, and often 
foliaceous at the sides, increasing in breadth from time to time, 
thickening internally. The shell is often camerated, or becomes 
spongy and loose in texture, and subject to the attack of many 
lithophagous annelids, and boring sponges. 
In shape the shell is variable, mostly rounded, or if the apex 
is produced, pyriform. The round form frequently becomes 
falcate, the lower portion curving, usually to the left. This is 
very noticeable in the 0 . estuarii group. The curvature and 
position of the apex, whether turned to the left (its normal place) 
or to the right, does not seem material to the growth of the 
mollusc, its position being determined by the way the spat falls. 
The umbo of the lower valve is frequently elongated in old shells, 
and is mostly chambered. 
The ligamental area in the type 0 . edulis and its allied forms 
is trigonal, enlarging with age and exhibiting lines of accretion 
in normal conditions, but is subject to the mode of growth by 
the umbo, sometimes becoming long and attenuated. 
The disposition of the ligamental area and the apex has little 
relation to the rest of the shell, except so far as the body position 
of the animal is concerned, the position of the adductor scar 
agreeing with the right or left inclination of the apical portion 
of the shell. The thickness of the aged or enlarged apex is 
illusory, as in one Selsea Bill shell, with area 25 mm. long, and 
12 mm. thick, it is made up of hollow concamered chambers. 
Having attained maturity, the animal ceases to grow bodily, 
but enlarges the shell by the deposition of additional shelly matter, 
seeming as if it shrank itself in the process of doing so. The 
so-called bottom valve in deep water individuals is not infre¬ 
quently coated with masses of Serpulas and Balani, parasites 
seldom seen on the flat valves. 
OSTREA EDULIS Limit . 
While all writers agree that Linne uses the name ostrea edulis, 
some of them differ as to which of its numerous varieties he 
referred to. His diagnosis (Syst. Nat., x., p. 699, 1758) “ testa 
