198 
recorded in subsequent ones. Earliest record, June 17, at 76°; and 
latest, October 2, at 63°. Always present in small numbers and 
evidently adventitious. 
Cathypna luna (Ehrbg.) Gosse.—Average number, 47. Found 
in every month but November, though always in small numbers and 
irregularly. All but six of the thirty-three records fall between 
April 1 and October 3 and above 50°. Over half of all the individu- 
als were found in 1896. This fact, together with the nature of the 
seasonal distribution, indicates plainly its adventitious character. 
Cathypna rusticula Gosse.—Found once, March 22, 1897, at 44°. 
Not previously reported from American waters. 
Celopus porcellus Gosse.—Average number, 106. From March 
to September, at 37° to 80°, and apparently adventitious. 
Colurus bicuspidatus Ehrbg.—Average number, 274. This 
Species is apparently a winter planktont. In 1897 it appeared first 
November 9, at 50°, and was found somewhat irregularly through 
the winter until May 17, at 64°. There is a pulse March 15, at 
46°, of 6,400. Ovigerous females were found during the rise of the 
pulse, and males on April 12, on its decline. A few scattered records 
were made in the following winter, beginning November 8, at 46°. It 
occurs in the plankton during flood season and may be adventitious. 
Colurus obtusus Gosse.—Average number, 38. In small numbers 
and irregularly in March and April at temperatures below 50°, and 
in September at 73°. Hempel (’99) lists also C. deflexus Ehrbg. 
Diglena circinator Gosse.—Average number, 121, 1n 1896; a year 
when many adventitious rotifers were brought into the plankton 
by disturbed hydrographic conditions. All the records lie between 
April 29, at 70°, and July 28, at 81°. Anovigerous female was found 
in July. The species is adventitious in the plankton. 
Diglena forcipata Ehrbg. was recorded once—October 12, 1897, 
aioe 
Diglena giraffa Gosse was observed but once in the river plank- 
ton. Not before recorded from American waters. 
Diglena grandis Ehrbg. was recorded in July and September at 
7Osanda/9~. 
Diglena uncinata Milne was found August 12, 1898, at 82°. 
Hempel (’99) reports D. biraphis Gosse and D. catellina Ehrbg. 
in waters immediately tributary to the river. All members of the 
