722. REPORT OF COMMISSIONER OF FISH AND FISHERIES. [40] 
erenatus), with tent-shaped, calcareous shells and tendril-shaped feet, often 
cover the entire surface of one of the valves. Frequently the shells are 
bedecked with yellowish tassels a span or more in length, each of which 
is acommunity of thousands of small gelatinous bryozoa (Aleyonidium 
gelatinosum), or they are overgrown by a yellowish sponge (Halichondria 
panicea), whose soft tissue contains fine silicious spicules. Upon many 
beds the oysters are covered with thick clumps of sand which are com- 
posed of the tubes of small worms (Sabellaria anglica). These tubes, 
ealled ‘‘sand-rolls,” resemble organ-pipes, and are formed from grains 
of sand cemented, into shape by means of slime from the skin of the 
worm. The shell forms a firm support upon which the worms can 
thus live close together in a social community. Upon certain beds near 
the south point of the island of Sylt, where the finest-flavored oysters 
of our sea-flats are to be found, there lives upon the oyster-shells a 
species of tube-worm (Pomatoceros triqueter) whose white, calcareous, 
three-sided tube is very often twisted about like a great italic S. The 
shells of many oysters upon these beds also carry what are called “sea- 
hands” (Alcyoniwm digitatum), which are white or yellow communities of 
polyps of the size and shape of a-clumsy glove. Often the oyster- 
shells are also covered over with a brownish, clod-like mass, which con- 
sists of branched polyps (Hudendrium rameum and Sertularia pumila), 
or they may be covered with tassels of yellow stems which are nearly 
a finger long and have at their distal ends reddish polyp-heads (Tubu- 
laria indivisa). Among these polyps, and extending out beyond them, are 
longer stems, which bear light yellow or brown polyp-cups (Sertularia 
argentea). Within the substance of the shell itself animals are also found. 
Very often the shells are penetrated from the outside to the innermost 
layer, upon which the mantle of the living oyster lies, by a boring sponge 
(Clione celata), and in the spaces between the layers of the shell in old 
oysters is found a greenish-brown worm (Dodecacerea concharum), armed 
with bristles, and bearing twelve large tentacles upon its neck. I 
once took off and counted, one by one, all the animals living upon two 
oysters. Upon one I found 104 and upon the other 221 animals of 
three different species. The dredge also at times brings up fish, 
although it is not very well adapted for catching them. Soles (Platessa 
vulgaris), which seek by jumping to get out of the vessel and once more 
into the water, stone-picks (Aspidophorus cataphractus), and sting-rays 
(Raja clavata), which strike about with their tails, are abundant upon 
the oyster-banks. Besides those already mentioned, there are many 
other larger animals which are taken less frequently in the dredge. 
There are also a host of smaller animals covered up by the larger ones, 
and which can be seen only with a magnifying glass. Very few plants 
grow upon the banks. Upon only a single one of the oyster-beds of the 
sea-flats has eel-grass (Zostera marina) taken root. Upon other beds 
reddish-brown alge (Mloridie) are found, and, floating in the water which 
flows over the beds, occur microscopic alga (Desmidie and Diatomacee), 
