294 GARY N. CALKINS 



lateral cilia, the multiple macronuclei, and the tapering posterior 

 end with a broad point. Less important characteristics are the 

 size, the exact number of macronuclei, and the position of the 

 contractile vacuole. (Engelmann does not mention the con- 

 tractile vacuole in his description, but in the two figures which he 

 gives it is represented as a simple spherical vessel lying in the 

 posterior part of the anterior third of the body.) 



The New York variety differs in respect to these minor char- 

 acteristics as indicated in the following description : 



New York variety of Uroleptus mobilis. Body form constant, 

 plastic, circular in section (figs. 1, 3); about 10.5 times longer 

 than broad (based on averages of measurements of length and 

 of breadth at center of body) , and tapering gradually to a broadly 

 pointed posterior end. The posterior end is permanently curved 

 towards the ventral side. (Engelmann does not mention this 

 curvature, but represents it in his figure.) The lateral cilia are 

 long and distinct and sparsely distributed along straight rows 

 running from end to end and around the posterior end of the 

 body. Owing to density of the protoplasm, the ventral cilia 

 cannot be made out on the living organism, but in cross-sections 

 it is evident that three rows of ventral cilia are present, and 

 that they are finer and shorter than the lateral cilia (fig. 3). 

 The frontal cirri, three in number, are placed in an oblique row 

 at the extreme anterior end of the ventral surface. The tenni- 

 nal cilia of the ventral rows are conspicuous at the anterior end 

 and give the impression of five or six frontal cirri. 



The peristome occupies about one-sixth of the entire length 

 of the body and this region is slightly flattened. The peristome 

 is very narrow with an obliquely curved row of powerful pyra- 

 midal membranelles on the left side, but almost filling the peri- 

 stomial area. The right margin is sharply cut with a narrow un- 

 dulating membrane inserted between it and the adoral zone 

 (fig. 2). 



The macronuclei are eight in number, and, in the vegetative 

 stages, each possesses a typical nuclear cleft. The micronuclei 

 are variable in number from two to six. They are minute and 

 homogeneous. 



