196 THE ESSEX NATURALIST.
I owe to the courtesy of Dr. C. T. Trechmann the loan of a
fine specimen (plate xii., fig. 3), dug up in Hartlepool Harbour at
8 feet depth in sandy clay, measuring 4 by 41/2 inches, with a com-
bined depth of 2 inches. This example exhibits the yearly accre-
tion of surface, there being about 40 growth lines in each valve.
Jeffreys' shell was evidently an aged example, and my own
impression is that any healthy and well-nourished oyster,
enjoying a quiet life in deep water amidst congenial surroundings
may develop into the hippopus state. How long an oyster
lives is uncertain. Prof. Moebius states that, although rarely
met with, he had seen specimens between 25 and 30 years old,
but if thickness and number of layers is any criterion, they
certainly live to a more advanced age than that.
Deep-sea, or "trawlled" oysters range from the Varne and
Ridge Shoals in the English Channel to Burnham, in Norfolk, and
the North Sea, and are a rugged type of shell, averaging 4 by 31/2
inches of good size. Shells from near the Dogger are usually
very irregular in outline, undulated in every direction with
numerous excrescences. They are long in proportion to breadth,
and deep. One in my collection, 5 by 31/4 inches, has a depth of
13/4 inches in the very convex under valve.
Lamarck located his species from Boulogne to La Manche,
and Dautzenberg et Durouchoux (Feuille. des Jeun. Nat., 1914,.
vol. 44, p. 48,), say that the young shells they found affixed
to rocks and stones in the Bay of St. Malo, probably belong to
the hippopus distinguished by "ses cotes rayonnantes nombreuses
et saillantes." Various forms have been associated with the name
hippopus by Messrs. Praeger, Marshall, and the Roussillon
authorities.
Lamarck specially notices that O. hippopus is not so good to
eat nor so digestible as O. edulis, but whether this is a test of
specific value has yet to be decided. Gastronomes of all periods
have noted this variation of flavours, from the days of Juvenal
onwards. Walfleet near Colchester was noted as early as.
1622. Drayton (Polyolbion) writes of them "Think you our
oysters here unworthy of your praise." T. Flatman, 1674.
(Belly Gods) thought so, apparently—"Your Wall Fleet oysters
no man will prefer before the juicy grass-green Colchester."
Most of the oysters sold at Stourbridge fair, near Cambridge, seem
to have been of this type, as it is recorded in Hone's Everyday