288 
mum record. Their fluctuations are erratic, and show no apparent 
relation to hydrographic or other environmental changes. 
Lampstlus anodontoides (Lea) Baker.—Glochidia referred with 
some uncertainty to this species appeared somewhat irregularly in 
the plankton in small numbers in September—December and again 
in June-July. The seasonal distribution in two periods suggests 
the inclusion of two species. 
Arcidens confragosus (Say) Simpson.—Glochidia of the type 
referred by Lea to the old genus Margaritana, and presumably 
belonging to this the commonest member of this genus (as formerly 
understood) in our locality, were taken in the plankton December 
18, 1895, in small numbers. 
BRYOZOA. 
This group is represented in our plankton by the floating stato- 
blasts, when these occur, as in Pectinatella and Plumatella, by 
detached and floating fragments, as in Urnatella, or by natant 
colonies, as in Lophopus and Cristatella. Genera such as Fredericella 
and Paludicella, whose statoblasts sink, fail to appear in the plank- 
ton, though in some cases they may be abundant in the bottom 
fauna. The Bryozoa are plankton feeders, and play an important 
role as plankton reducers in vegetation-rich backwaters. 
DISCUSSION OF SPECIES OF BRYOZOA. 
Cristatella mucedo Cuvier.—This species was found in the back- 
waters in summer months, especially in Quiver Lake. Statoblasts 
probably referable to this species occurred sparingly in May and 
August. 
Lophopus cristallinus Pallas.—This rare bryozoan occurred in 
the channel plankton, though not in our quantitative collections, in 
July, 1897, in that part of the channel containing the discharge from 
Quiver Lake. Small, free-swimming colonies of 5-50 zooids were 
taken in surface waters. 
Pectinatella magnifica Leidy.—Statoblasts of this superb bryo- 
zoan were not uncommon in the backwaters, and were seen several 
times in the vernal plankton of the channel. The large floating 
colonies are found near the surface in July—October in the open 
backwaters, and more rarely in the river itself. The translucent 
Goa = 
