BRITISH OYSTERS : OLD AND NEW. 209 
appressed. My largest example measures, length 130 mm., 
breadth 140 mm. ; my smallest (plate xvi., fig. 18), 3 by 2 \ 
inches, the lower valve expanding at the shoulders to 3 J inches. 
Many of these Western forms attain a great size, height 5J to 
6 inches, breadth 4J inches, and are round and solid ; the ribs or 
folds on the lower valve being narrow to moderately broad, 
so that, when the concentric laminae are raised, as they usually 
are, the interrupted ribs become vaulted or fimbriated, especially 
so in Jersey shells. The corneous plates in the upper valve 
are broadly laminate, and extend considerably beyond the 
margins of the valves. 
Da Costa’s notice of the growth of the lamellar horny plates 
is very clear and may be quoted here (British Conchology, 1778), 
as it so exactly describes the ornament and growth of the Western 
oyster. “ Usually about 3 inches long, and less in breadth, the 
shells vary in size and shape from their adhesion to other bodies 
in different places. 
“ The upper or flat valve is of a dirty brownish hue, roughly 
plated or made up of transverse flakes exceedingly thin. These 
lie close, compact and strongly set together on the upper part, 
well towards the middle of the shell, from thence to the bottom 
they are more loosely set, become finer and thinner, and more 
extended beyond one another. As they approach the lower 
margin they are generally so. loose, separate and extended, 
as to foliate the shell very finely, even much beyond the edges 
of it. 
“The under valve is very rugged, whitish or generally greenish; 
the leafed structure seldom shows such fine foliations as the • 
upper valve ; these are chiefly apparent on the edges of the 
wrinkles that cross the shell, which they furbelow or plait. These 
are commonly of a purplish colour; the valves wrought with 
several irregular, prominent, longitudinal ribs.” 
Forbes and Hanley (Brit. Moll, ii., p. 307, pi. liv.) notice the 
“ dissimilarity of aspect between the sleek looking valves of the 
flattened native oyster of our markets, and the more coarse (!) 
and rugged, but far more beautifully sculptured and coloured, 
solitary individuals which are ordinarily termed rock oysters.” 
The shell figured by these writers is very different from that of 
Jeffreys (op. cit., fig. 1), and represents a shell not very common 
in the cabinets of collectors. Their description reads like an 
