460 Wisconsin Academy of Sciences, Arts, and Letters. 
The corona is frontal and consists of a circumapical band of 
cilia with two strongly developed lateral, auricle-like tufts of cilia 
adapted to swimming; the buccal field is evenly ciliated and the 
mouth is near the ventral edge of the corona. 
The mastax is virgate and the trophi of very simple form. The 
rami are approximately triangular, strongly curved longitudinally 
and have large, rounded alulae. The fulcrum is a very long, slen¬ 
der, tapering rod, incurved and slightly expanded at the posterior 
end. The unci are triangular plates with one weak ventral and 
a rudimentary second tooth; additional teeth are represented by 
three faint striae. The manubria are long and double-curved, 
tapering gradually from the broad base to the posterior end; near 
mid-length there is a small projecting lobe on the ventral edge; 
their longitudinal direction is nearly at right angles to the fulcrum. 
Two small curved rods are imbedded in the anterior walls of the 
mastax and serve to support the edges of the mouth during the 
pumping action. 
The oesophagus is short and slender. The gastric glands are 
elongate oval and strongly compressed laterally. There is no con¬ 
striction separating the stomach and intestine. The ovary is 
large and of a somewhat irregularly oval outline. A small bladder 
is present. The foot glands are very long and nearly cylindric; 
they discharge into a large mucus reservoir at the base of the toes. 
The ganglion is large and saccate, reaching nearly to the pos¬ 
terior end of the mastax. No retrocerebral organ is present. The 
eyespot is at the extreme end of the ganglion and consists of a 
very small sphere of minute pigment granules. 
Total length 225-250yLt; toes 12/x; trophi 32/x. 
Pleurotrocha petromyzon is cosmopolitan in its distribution, but 
does not usually occur in large numbers. It has been reported as 
attaching itself to other living organisms (Infusoria, Entomos- 
traca); we have not observed it in this condition and do not know 
under what circumstances it occurs. It is evidently not a case of 
parasitism, in the proper sense of this word, but rather one of 
synoecia or “ Raumparasitismus ”; the rotifer obtains free trans¬ 
portation and probably nothing more. The highly developed foot 
glands point to the possibility of an adaptation of this kind; they 
are found in all rotifers that are known to be synoecious or pseudo- 
parasitic. 
