MOLLUSCS, VERMES AND HYDROZOA 



FIG. 



Sftk^rium striatinum. 

 Enlarged. 



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. i8i, has thin rounded-oval, pellucid, somewhat 

 inflated valves with the umbones central and inwardly incHned. In the 

 adult, they are of light-greenish horn-color and in the young a very light 



yellowish color, and are J^ inch long, | inch broad 

 and I 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 

 related to S. cornea of Europe resembling it in size, 

 shape and generally in color. 

 Other locally distributed Sphseriums are S. rhomboidium, S. tenue and 

 S. truncatum. Both the described species survive in the aquarium. 



PisiDiUM. 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 

 i^ 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, 4 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 

 considerably resembles P. conicum of Europe. 



Other Eastern States species are P. abditum. Fig. igS, P- aquilaterale, 

 P. ferrugineum and P. ventricosum, all still smaller than the foregoing and 

 so tiny as to be of no considerable value to the aquariist- 

 Unio. 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, algse, infusoria and 

 other water animalculas. Their shells often contain 



FIG. 183. Pisidium ahditum. i • i i i r • i 1 J "11 



Enlarged. pearls, either attached or tree in the muscle and gills. 



FIG. 182. Pisidium compressum. 

 Enlarged. 



241 



