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. 



Cathy pna 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. 



Ccelopus 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, in 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. An ovigerous female was found 

 in July. The species is adventitious in the plankton. 



Diglena forcipata Ehrbg. was recorded once October 12, 1897, 

 at 65. 



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 

 76 and 79. 



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 



