458 Wisconsin Academy of Sciences, Arts, and Letters. 
The corona is slightly oblique and consists of a marginal wreath 
of cilia with lateral, auricle-like tufts of long cilia adapted to 
swimming; the apical plate is unciliated and the buccal field evenly 
covered with short, close-set cilia; the mouth is near the ventral 
edge of the corona. 
The mastax is virgate and the trophi very simple; the fulcrum 
is long and rodlike, the rami triangular, curved and not denticulate; 
the manubria are very long and the basal plate much reduced; 
the unci are feeble and have only a single distinct tooth; the 
piston is very large. 
The eyespot is single and at the posterior end or on the lower 
surface of the ganglion; there is no trace of the retrocerebral 
organ. 
Type of the genns.—Pleurotrocha petromyzon Ehrenberg. 
This genus was created by Ehrenberg for P. petromyzon, which 
he supposed to be without an eyespot. When the error was dis¬ 
covered, he transferred this species to his ‘ ‘ Noah’s Ark, ’ ’ the genus 
Notommata, into which he thrust all illoricate, freeswimming roti¬ 
fers with cervical eyespot. He then proceeded, in accordance with 
his usual custom, to use the generic name for other species with¬ 
out eyespots and subsequent authors have followed him in this 
change of concept. As P. petromyzon does not belong to Notom¬ 
mata as now understood, the original generic name must be used 
for it, and the obscure species later referred to Pleurotrocha, listed 
below, must be placed on a firm foundation or dropped as insuffi¬ 
ciently described. 
Pleurotrocha aurita Bergendal, Acta Univ. Lundensis, vol. 28, 1892,'sect. 2, 
No. 4, p. 49, pi. 2, fig. 15. 
Pleurotrocha constricta Ehrenberg, Abh. Akad. Wiss. Berlin (for 1831), 
1832, p. 129; Infunsionsthierchen, 1838, p. 419, pi. 48, fig. 1.— Hudson and 
Gosse, Kotifera, 1886, vol. 2, p. 19, pi. 18, fig. 3.— Von Hofsten, Arkiv 
Zool., Stockholm, vol. 6, No. 1, 1909, p. 12. 
Pleurotrocha gibba (Ehrenberg). 
Eydatina gibba Ehrenberg, Abh. Akad. Wiss. Berlin (for 1831), 1832, 
p. 127. 
Pleurotrocha gibba Ehrenberg, Infusionsthierchen, 1838, p. 418, pi. 47, fig. 
4.— Hudson and Gosse, Rotifera, 1886, vol. 2, p. 20, pi. 18, fig. 5. 
Theora gibba Eyferth, Mikroskopische Siisswasserbewohner, 1877, p. 51; 
Einfachsten Lebensformen, 1878, p. 83; 1885, p. 108. 
Pleurotrocha renalis Ehrenberg, Monatsber. Akad. Wiss. Berlin, 1840, p. 218. 
