380 



to the inhabitants of the bottom muds of our larger streams under 

 present-day conditions. 



PLANARIANS 



Various unidentified species of planarians, attached to shells, bits 

 of bark, leaves, etc., were not uncommon in Peoria Lake bottom hauls 

 in years previous to 1930. These did not appear in any of our 1920 

 or 1922 bottom dredgings, or on any of a quite large number of dead 

 mussel shells examined in the summer of 1920, although a few were 

 noted in sediment samples caught in the relatively fast current at 

 Peoria Narrows in August 1923 by a machine set about eighteen inches 

 above the bottom. 



BRYOZOA 



While only a single species of bryozoan, Plutnatella prin-ceps, var. 

 fruticosa, was found in Peoria Lake bottom collections in 1920 or 1922, 

 two other species, Paludicella ehrcnhergii Van Beneden and Uniafclla 

 gracilis Leidy, were common on live or dead shells in the deeper water 

 everywhere below Chillicothe up to the summer of 1915. On many 

 of the mussel shells examined in the summer of 1920 there were marks 

 apparently left by the attachment of former colonies of these species. 



SNAILS 



The list of snails missing since 191.5 includes two conspicuous 

 cases of large and abundant kinds which were formerly so common 

 in collections nearly everywhere in the lake that they gave their char- 

 acter largely to the majority of hauls made between Chillicothe and 

 Peoria in 1913 and 1915. These were Vivipara contectoides W. G. 

 Binney and Lioplax subcarinatus Say. 



Species of snails that occurred in smaller numbers, but which 

 seem to be of scarcely less importance as index organisms, include a 

 second large species of Vivipara, V. subpurpurca Say, which was taken 

 several times in the earlier collections, only in the middle and lower 

 lakes, and principally in the lower. Notable also, up to 1915, vvas the 

 little Amnicola cmarginata Kiister, which, although not widely dis- 

 tributed, occurred before 1930 in fairly large numbers over limited 

 areas in both the middle and lower lake. 



Two species of Valvata, V. tricarinata Say and V. bicarinata Lea, 

 were formerly not far from equally common in the wide waters of 

 the first two of the lakes. The first one was taken in a single haul 



