Dr. C. A. Kofoid on Platy.loiiua. 543 



On August 2, laSfi, l^-ofesaor II. Garimiii, while con- 

 ducting a biological survey of the aquatic lite in tho vicinity 

 of Quincy, 111., in tho bottoms of the Mi.ssis3ip])i River (see 

 Garman, 1890), found a specimen of this interesting species 

 in the waters of Liljhv Lake, lie records and sketches it in 

 notes now on file at this Laboratory, but published nothing 

 concerning it. 



The occurrence of this tiew genus in the waters of the 

 Wabash, Illinois, and ^lississippi River systems, and its 

 recurrence in our collections for several successive years 

 indicate its wide distribution and firm establishment in the 

 Mis.si.-;.si|)pi Valley in waters of some permanency. It has 

 not yet been noted in temporary pools. 



The associates of Plati/dorina in the plankton have varied 

 with the season, the locality, and the year. It may be said, 

 in a general way, that the plankton in which it occurs is 

 characterized by an abundance of Hagellates, of rotifers — 

 especially Brachionida^ — and of immature ('opepoda. A 

 water-bloom, composed largely of Eiigleaa, Trac'ielomonas, 

 Carfen'a, and other green flagellates, often appears at the 

 suiface of waters where Flatydorina is abundant. Goni'urn 

 is frequently associated with it in large numbers, as are also 

 Pandorina, iLudonna, and Pleodorina, though these three 

 genera may also be plentiful in the early summer, when 

 Platydorina may be absent or rare. Pleodorina californica 

 was extremely abundant in Salt Fork in August, but had 

 almost entirely disappeared by the time that Platydorina liad 

 reached its maximum. A few specimens of Voloox, which, 

 in this locality, is common in the spring months, were also 

 noted, while perhaps the most interesting associate in Salt 

 Fork was Ceratiiun kumaonense, discovered by Carter (1871) 

 in Ilindostan. Other chlorophyll-bearing associates fre- 

 quently seen are Pediastrum, IScenedesnius, Actinastrum, and 

 Closterium. Among the diatoms, Melosira, F'/ayillaria, and 

 Surirella were to be seen ; and among the Peridinidie Peri- 

 di'nium tahulatum was almost always represented. 



The zobplankton associated with PLitydorina is not less 

 varied than the phyto})laMkt()n. The Protozoa were usually 

 represented by Arcclla, Dlffiuyia, and occasionally by pelagic 

 Amaba; by Synura, Mallomonas^ Jh'nobryon, and U'rot/lena ; 

 and by Codonella and Coleps. Among the Rotiftra the order 

 Ploima was will represented; 7ViarMra and the Brachionidse 

 — notably Brachionns miUtaiis^ P. anyularis, B. jmnctatus, 

 and P. haktvi ami its varieties — were most common during 

 the summer months, while the SynclKetida3 increase in numbers 

 in the earlv autumn. I'olyart/ira was frequently al)uudant, 



