86 



leaving a groove in the mud Ijehiud them. In suitable places 

 in quiet water they may become very abundant, forming 

 what are known as clam Vjeds. The food of some of our species 

 consists entirely of microscopic plants and animals, such as algse 

 and protozoans. Some of the unios are very probably scavengers, 

 if we may decide from the condition of food in the stomachs of 

 alcoholic specimens. In winter our species jjrobably all go into 

 the mud at the bottom of the'' streams and lakes, and there 

 remain torpid until spring. The young are very different from 

 the adults, and some of them were formerly supposed to be dif- 

 ferent animals,— a mistake due to their ha\ang been found adhering 

 to aquatic animals of other kinds by means of a couple of strong 

 hooks with which the valves of the shell are furnished. For a 

 considerable time after leaving the egg they are retained in the 

 gill-pouches of the parent clams. 



Their interest, viewed either from the standpoint of the fish- 

 culturist or from that of the scientist, is very great. As Prof. 

 Porbes has shown in his papers on the food of fishes, they con- 

 stitute a large item of the food of some of our best fishes. The 

 great abundance in which they occur in the water of this region 

 must give them a decided influence, as competitors for food of 

 jnumerous other animals. 



Of the two families represented in the Quincy collection, the first 

 is represented by small species which commonly pass for the 

 young of the true clams (Unionidse) of the second family. That 

 they are adult animals is, however, easily shown with a magnify- 

 ing glass, since by its means they may be seen in many cases to 

 ■contain living young of relatively large size. The shells of these 

 bivalves are not commonly more than half an inch in length. 



Family CoRBicuLiDiE. 



Sphcerium solidulum, Prime. 



{Cyclas solidula, Prime, Proc. Bost. Soc. Nat. Hist., iv., 158, 

 1851.) 



Common in shallow water in Willow Slough. 



SphcBrium transversum, Say. 



•( Cyclas transversa. Say, New Harmony Disseminator, ii, 346, 1829. ) 

 Frequent in^ several of the pools. 



Localities: Willow Slough, Long Lake, Broad Lake, Wood 

 Slough. 



Family IJNiONiDiE. (Eiyer Clams.) 



Anodonta grandis, Say. 



{A. grandis, Say, New Harmony Disseminator, i, 341, 1840.) 



This large, smooth, thin-shellcd clam is common in most of the 

 sloughs and lakes. It is probably the species which the channel 



