218 
PuLses OF TRIARTHRA LONGISETA. 
Year Date Temp. No. Date Temp. No. Date Temp.| No. 
1394. | ———._ | —— | ——— | ——— | ——]| —— 
1895 Apr. 29 | 64° 29330) SS ee ee 
1896 Apr. 29 70° 5,556 SSS === —<——— June 11 YE 4,000 
ee SST 80° 6,000 
1897 =e ad SSS May 25 66° 8,800 —> — 
1898 SSS == aS May 10 62° 38 , 400 June 28 78° 800 
fay eal 70° 1,000 
Year Date Temp. No. Date Temp. No. Date | Temp. No. 
1894 Aug. 15 84° i SSIY/ =— 
1895 July 18 80° 19,080 Aug. 21 82° 10,683 Sept. 12 79° 2,336 
1896 |-July° 6 | 80° 2,800 | Aug. 8 | 86° 7,200 | ——— a 
1897 July 21 81° 49 ,600 Aug. 17 79° 9,600 Sept. 7 80° 70,000 
1897 Ofer, 5 ult 8,000 = = = —— 
1898 July 26 89° 28,000 Aug. 30 83° 6,400 Sept. 27 163° 14,400 
This is an exceedingly variable species. It varies in the relative 
length of the three long sete, in their spinosity, and in the location 
of the posterior one. Many of the individuals in our waters resemble 
the form described by Plate (’85) as T. terminalis. The long-spined 
form described by Zacharias (’94) as var. limnetica is also abundant. 
It is doubtful if either form is worthy even of varietal distinction. 
This species has been reported only from Lake Erie and the 
Illinois River in this country, and seems to be rare in the former. 
Weber (’98) finds it abundant in the plankton of Lake Leman; 
Burckhardt (’00 and ’00a) reports it as wide-spread and almost 
perennial in Swiss lakes, but with its maximum in December— 
February, and slight development during warmer months. Borge 
(’00) finds it to be one of the common rotifers in the summer plank- 
ton in Sweden; Marsson (’00) reports its perennial seasonal range in 
several German waters, with greater numbers during the warmer 
season. Apstein (’96) gives it a perennial distribution in Lake 
Pl6n, with larger numbers in June-November, and maximum in 
June-July or August. According to Seligo (’00) the species is per- 
