
MOLLUSCS, VERMES AND HYDROZOA 

The interior has a chalky white margin and bluish-white nacre, overshot 
with delicate shades of green. The mature mussel is 2% inches long, 114 
inch broad and 1 inch thick at the umbones. It is not as generally dis- 
tributed as the foregoing, but may be found in almost all the river systems 
of the Eastern and Middle States, a Western species being M. truncata. 
GENERAL Remarks. What has been stated as to the colors of snail 
shells also applies to mussels. The presence of metallic oxides in the 
water affects the color and acidities erode the valves, principally on the 
umbones, the older portion of the valves; and when this has progressed 
to the extent of perforating the valves the mussel dies. 
Best Aguartum Mussets. Nearly all the mentioned species will 
thrive in the aquarium, instances being known of remarkable longevity. 
Spheerium, Lampsilis and Margaritana will survive for years; some in the 
author’s household aquaria at this writing having done most effectual duty 
as scavengers for three and a half years and are still active and of good 
appearance. The introduction of one mussel into the aquarium for each 
8 or 10 gallons of water is to be recommended, but watch should be kept 
until they become acclimated, after which an occasional tap on the valves 
will give assurance that they are alive. They are the best means of eradi- 
cating the objectionable Tubicolores worms. If they die, the decay is rapid 
and will cause trouble in the aquarium. 
FRESHWATER VERMES AND HYDROZOA 
Tusicota AND Hypra. In addition to the already described low 
forms of animal life in the aquarium the freshwater Worms and Polyps 
should be mentioned. The eggs, spores or young are introduced with 
the water supply, in pond mud and on the aquatic plants. They may 
increase to such numbers as to become objectionable, as the worms bring 
the soil and humus to the surface of the pebbles, and by their constant 
activity cause turbidities in the lower water levels; and the polyps become 
active enemies to the spawn and young fishes. 
FresHWATER Worms. ‘These belong to the order Annelida. The 
most usual forms are Pristina leidyi and Stylaria lacustris which live in the 
soil and mud. Lumbriculus limosus, about 2 inches long, and Nais 
rivulosa, about 5% to 34 inch long, live in the axils and under the leaves ot 
aquatic plants. Of the Tubicolous worms, the objectionable Trimnodrilus 
is usually the only species present. As of these all but the last named 
are eaten by the fishes, no further mention is necessary. 
Timnodrilus claparadii, Fig. 192, and T. montanus are not eaten by 
goldfishes and may increase to such numbers that the whole bottom of the 
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