18 THE NAUTILUS. 



mussel. Kofoid took his plankton by means of a pump, and 

 at all depths, from near the bottom to the surface. He may, 

 therefore, have obtained his glochidia anywhere between 

 those extremes of depth. 



During the spring and summer of 1920, in an attempt to 

 ascertain the relation, quantitatively and qualitatively, be- 

 tween the river, the reservoir and the various ponds of the 

 Fisheries Biological Station at Fairport, Iowa, occasional 

 surface towings were made with a fine bolting-cloth net in all 

 the places mentioned. On April 12, ten short hauls were 

 made at the surface of the Reservoir near its outlet, in about 

 12 feet of water. In the portion of the haul examined (in 

 most cases, especially where a considerable amount of mate- 

 rial was taken, only a small portion, usually about one-tenth, 

 \vas examined carefully) a glochidium of the Anodonta type, 

 probably that of Anodonta corpulenta, was taken. It was at 

 first supposed that it was dead, but four hours after capture 

 it was observed to snap its valves. 



On July 3, the river, which was high and muddy, showed a 

 slightly greenish cast, suggesting an abundance of plankton. 

 Accordingly several short draws, almost dips, were taken at 

 11 : 15 a. in. from the end of the pier, from the surface in 

 shallow water near shore. One glochidium, provisionally iden- 

 tified as that of Lampsilis anodontoides, and 12 shorter, 

 rounder, probably of some species of Quadrula, were taken. 

 On July 29 a towing was taken in water a considerable dis- 

 tance from shore, from a boat and in the current. Only a 

 small amount of the material mostly silt was examined ; 

 but in the part scrutinized was found a glochidium. 



On July 30, the townet was held under the edge of the mass 

 of water coming up from the river and falling in an inverted 

 bowl-shaped mass from the vertical inlet pipe, where it enters 

 the Reservoir. The net was held here only about 3 minutes, 

 and naturally strained only a small portion of the water fall- 

 ing from the pipe hardly a hundredth part. A good deal of 

 material, chiefly detritus, was obtained and only a small 

 amount of this examined ; but in this small amount was ob- 

 tained 8 glochidia of the Lampsilis type. 



