370 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
ditions. For it may be found that (1) many .shells are, if anything, less plicate than 
in some types of raccoons; (2) the plication may increase in number from three, 
angularly marked, to a dozen or more, faintly suggested; (3) the younger oysters are 
often comparatively smooth in shell characters. 
The oyster industry in Portugal is remarkable, inasmuch as it is prosperous 
although practically unprotected by law. Oysters are abundant and low in price, a 
result, however, which could never have been obtained had the demand been great 
enough to render it profitable to introduce improved dredging apparatus, with 
perhaps a consequent industry of canning. No canning factory, it is said, exists in 
Portugal. Lack of demand has also tended to deter innovations in culture. 
OYSTER-CULTURE IN GERMANY. 
In Germany, oyster-grounds exist in only a single district, the sheltered corner of 
the North Sea, where the coast line has almost reached the frontier of Denmark. As 
this area of natural production is a very restricted one, it may reasonably be inferred 
that it possesses exceptional characters and conditions which render impracticable 
the introduction of the French system of oyster-culture. Such a conclusion has been 
firmly maintained by Prof. Mobius, who, as the state authority in these matters, 
studied the conditions of the industry when the question of replenishment of the oyster 
banks was being agitated. His chief works, Ueber Austern- und Miesmusclielzuckt 
(1870), Die Auster und die Austernwirthshaft (1877),* have become classic in the liter- 
ature of oyster-culture. If his conclusions be altogether accepted, a number of corol- 
laries to his proposition seem too important to be allowed to remain undiscussed. 
Thus, for example, it would follow that the success of the Dutch and French indus- 
tries was dependent on exceptionally favorable local conditions, and that, therefore, 
the introduction of artificial methods into a foreign country might not succeed even 
Avhen large natural oyster-grounds were in the immediate neighborhood, for it is to be 
remembered that the natural banks of Germany are the largest in associated series, if 
not the most productive, in all Europe. 
As to the conditions of the oyster banks : t They occur, as has been noted, in 
but a single district, a corner of the North Sea which has been cut off and sheltered 
by a barrier of fringing islands. This included area is about 50 miles long and about 
15 miles wide, extending due southward from the Danish frontier to beyond the line 
of the ancient town of Husum. Its sea wall, protecting not a little the low lying coast 
of Schleswig-Holstein from the storms of the North Sea, is formed principally of the 
three long, fringing islands, Eom, Sylt, and Amrum, in whose immediate lee occur the 
largest and most fertile of the oyster banks. The tranquil conditions which this con- 
siderable water area offered, with bays and sheltered coves, seem to have been from 
the earliest times not unfavorable to oyster growth; but doubtless its limits have been 
shifting and changing, tending to increase shallowness and to reduce the extent and 
sweep of its currents, and perhaps to make it less and less of an oyster sea. Its waters 
are not deep, the fall of tide averaging perhaps about 10 feet, at lunar tides becoming 
as great as 18 or 20 feet, and exposing hard sandy flats over the greater portion of its 
area. These have given rise to the name Wattenmeer (sea of flats or shoals). The 
flats occur largely on the side of the mainland, and the outrunning water, having to 
* Wiegandfc und Heinpel, Berlin, the latter translated in U. S. F. C. Rep., 1880, p. 83. 
1 Cf. Mobius, Die Auster und die Austernwirthsohaft, i. 
