204 
THE ESSEX NATURALIST. 
The upper valve exhibits numerous close-pressed fairly broad 
lamellar growths, the edges hardly rising above the flat surface, 
the umbonal area is usually depressed or flattened. Inside, the 
inhabited portion of the shell in the older examples is pyriform, 
becoming attenuated towards the wide and generally shallow 
ligamental area, terminating in an acute and sinuous point in 
the younger shell, and widening below in a posterior lateral 
direction. 
The variation in shape is due to the way in which the accre¬ 
tionary shell-matter has been disposed on the anterior side of 
the umbonal region (plate xiv., fig. 12) and this may extend to as 
much as ij inch beyond the natural margin of the inhabited 
portion ; the breadth over all may be from 3J to 5 inches, the 
narrowest shells being usually the longest. Inside the variation 
is much less apparent. Plate xiv., fig. 12, gives a fair idea 
of the habitable shell. 
A. S. Stewart was the first to call attention to these shells. 
In a paper published many years after its reading (Proc. Belfast 
Naturalists’ Field Club, vol. xx., p. 17) he mentions finding 
immense specimens of the solitary deep water variety of the 
oyster 0 . hippopus . Canon Grainger ( Dublin University Geol. and 
Bot. Proceedings, vol. 1, 1859), says the shells occur of immense 
size in innumerable myriads. The earliest figure I have seen of 
this type of oyster is in Brown’s Rec. Con. Gt. Britain (pi. xxii., fig. 
19), being that of an old Firth of Forth specimen. A thick bed 
of these shells occurs at Grangemouth, where the shells are large 
and solid to a degree seldom attained by the normal form in the 
present area. They also occur near Micklewood, five miles west 
of Stirling, under 18 feet of clay, but several feet above high 
water mark. Nordmann figures a shell of this kind from the 
Danish Middens. 
In the Nar Valley, Norfolk, at West Bilney and Narford 
“ large antiquated specimens are common ” (S. Woodward, 
Geol. of Norfolk). A specimen in the Museum of Practical Geology, 
London, measures 7 by 4 ins. in its dimensions, length of ligamental 
pit 2 ins., breadth 2Jins. Marshall and Praeger correlate the 
Irish shell with 0 . hippopus, but it does not agree with the 
North Sea shells, nor does it occur in the English Channel 
It may be noticed that all these deep estuary oysters are very 
dark in colour, almost black. 
