190 



FBESH-WATEE AQTIABIA. 



Sphserium rivicolum is found in the slow-running and 

 sometimes in tlie stagnant water of various parts of England, 

 and rarely in Ireland, but it is local. It is the largest of the 

 Sphxriidse, having a shell about fia. long, ^in. high, and fin. 

 thick. The body of the animal is grey, with a yellowish 

 tinge; the foot is a greyish- white ; the siphons are short, 

 nearly of the same length, and whitish. The shell is 

 globosely-ovate, solid, and of a greenish-brown colour, marked 

 with two or three darkish bands. The umbones are central 



^.' 



a." 



Fig. 125. Outline op Left Valve of Unio tumidus. aa. Length ; &!>, Height ; 

 c. Umbo ; d. Anterior Extremity ; e, Posterior Extremity ; /, v entral Margin ; 

 £r, Dorsal Margin ; A, Ligament ; i, Lunule. , ^ 



{i.e., in the middle), close to the dorsal margia. The hinge is 

 strong, and there are two cardinal and four lateral teeth. 

 The ligament is short and external, and the muscular scars 

 ai"e distinct. 



Sphserium. ovale is a small scarce mollusc, but it is of 

 interest in the aquarium. It is found in canals and ponds. 

 The body is white, .and the siphons are long and united 

 nearly as far as their tips. The foot is large and tongue- 

 shaped. The. shell is oblong, one extremity being rather 

 round and the other truncate. The umbones are a little in 



