92 BULLETIN OF THE BUREAU OF FISHERIES. 



consisted chiefly of the yellow mud of the river bottom, with organisms of any sort few 

 and far between. In general, mud" is an abundant element in the stomachs of all mus- 

 sels ; so much so that the color and general appearance of the mass of the stomach con- 

 tents of all river mussels examined was that of the bottom soil. In ponds full of dif- 

 fused plankton algae the plants may be present in sufficient quantities to at least fleck 

 the "ground color" with a pronounced green or blue green. Studies of the stomach 

 contents of the mussels in the reservoir of the Feeder Canal at Fort Wayne, in 190S, 

 revealed the presence of many flagellates, such as Trachelomonas and Phacus, together 

 with such minute plants as Scenedesmus, Pediastrum, Botryococcus, such diatoms as 

 Gomphonema, Navicula, and the like, a few desmids (Cosmarium), fragments of Cera- 

 tium hirundinella, casts of the rotifer Anurcea cochlearis, and small fragments of 

 confervoid algae. In the main current of the St. Joseph, St. Mary, and Maumee 

 Rivers there was much mud with about the same organisms scattered sparsely through 

 it. A mucket, Lampsilis ligamentina, taken in the Auglaize River, contained what 

 appeared to be bacteria. Mussels in Lake Amelia, near St. Paul, Minn., contained an 

 abundance of that peculiar organism Dinohryon sertularia. The mussels of Lost Lake 

 and Lake Maxinkuckee, Ind., contained enough plankton organisms of all the minuter 

 sorts to give the stomach contents a greenish cast or to mottle it considerably with greenish 

 flecks. Not to enter into too great detail, they contained such organisms as Microcystis 

 aeruginosa, Pediastrum boryanum, and P. duplex, Caelastrum microporum, Botryococcus 

 hraunii, Scenedesmus, Melosira crcnulata, Coconema cymhiforme, Navicula, Epithemia 

 argus, Fragilaria, Cocconeis pediculus, and Lyngbya cEstuarii. Melosira and SpiruUna 

 represented the longest filaments taken. A nurma cochlearis was common but represented 

 only by lorica, and Chydorus was the largest and most active organism taken. 



Observations believed to be of both interest and importance were made in the Mis- 

 sissippi in the late summer and autumn of 191 9. The river had remained high and 

 swift until about the beginning of September, when it fell rapidly. With its fall the 

 great body of marginal water lost the velocity of its flow, and great areas behind wing 

 dams, lagoons, and mouths of sloughs became extensive areas of calm. In these a rich 

 and varied plankton, consisting chiefly of holophytic sorts (Euglena, Pandorina, rotifers, 

 Platydorina, and a bottom benthos of diatoms) , rapidly developed in considerable quan- 

 tities. The stomachs of the mussels in the bottom of these areas of calm contained 

 numerous organisms of the plankton and benthos such as Anurcea cochlearis, Pandorina, 

 Mycrocystis, Scenedesmus, Phacus, and various diatoms; the stomach contents bore 

 general resemblance to those of the mussels of the Feeder Canal reser\^oir. 



Opportunity was taken to examine the stomach contents of some young mussels 

 which were obtained at the same time. In a slough sand-shell, Lampsilis jallaciosa, 

 19.1 mm. long, all that could be recognized was one colony of Clathrocystis. Another, 

 18.9 mm. long, contained chiefly brown, gritty mud in which were several Scenedesmus 

 caudatus, Phacus pleuronectes , i Coscinodiscus, a few very minute Melosiras, and some 

 rough spherical cysts. A third example, 19.6 ram. long, contained much brown flocculent 

 organic mud, a large colony of Microcystis, i Scenedesmus caudatus, the diatom Cyclotella 

 compta, and many of the green rough cysts. 



The stomachs of some very small Lampsilis arwdontoides and L. luteola, reared in 

 troughs at Fairport and apparently thriving, contained only a fine brown flocculent 



<> The mud is probably mixed with much decomposing organic matter. 



