
MOLLUSCS, VERMES AND HYDROZOA 

slothful in movement. — It is found in larger ponds and in rivers of the 
Eastern and Middle States and along the Lakes. This mussel is nearly 
related to S. rivicola of Europe, both in size and in the appearance of 
the valves. 
S. striatinum, Fig. 181, has thin rounded-oval, pellucid, somewhat 
inflated valves with the umbones central and inwardly inclined. In the 
adult, they are of light-greenish horn-color and in the young a very light 
= inch broad 
“ 5 
yellowish color, and are % inch long, 
and ; inch thick. The animal is of light pink color 
and its movements are rapid. Found everywhere 
in the mud of freshwater ditches and streams among 
the roots of water plants. This mussel is nearly 

FIG. 181. Spherium striatinum. Yelated to S. cornea of Europe resembling it in size, 
Sha ae shape and generally in color. 
Other locally distributed Spheriums are S. rhomboidium, S. tenue and 
S. truncatum. Both the described species survive in the aquarium. 
Pistpium. ‘These tiny mussels differ from the foregoing in having 
but one siphon and are more inclined to inequilateral forms; are not 
generally quite so thick and are of a lighter color. They vary from ; to 
14 inch in length, are never active, thrive well in the aquarium and often 
bury themselves for a long period. 
P. compressum, Fig 182, has solid, very oblique triangular inflated 
subequalateral yellow or grey valves with light-blue interior, a thick hinge 
having small cardinal and distinct lateral teeth. The umbones are prominent 
and placed a little prosteriorly and the valves have 
a slight beak, the posterior being evenly rounded. 
The lines of growth are concentric and finely marked. 
The valves are about { inch long, + inch broad 
and ;, inch thick. Found quite generally in the 
United States and is common to New England, 
New York, Pennsylvania and Ohio. ‘This’ mussel tie. rgz.. Piddium compreesum. 
considerably resembles P. conicum of Europe. ee 
Other Eastern States species are P. abditum, Fig. 193, P. equilaterale, 
P. ferrugineum and P. ventricosum, all still smaller than the foregoing and 
so tiny as to be of no considerable value to the aquariist- 

Unto. These most common freshwater mussels 
are to be found in ditches, ponds, lakes and streams. 
Their food is both vegetal and animal, as they subsist 
upon decaying vegetation, diatoms, alge, infusoria and 

other water animalcule. Their shells often contain 
FIG. 183. Pisidium abditum. : : : 
Enlarged. pearls, either attached or free in the muscle and gills. 
ear 
