THE OPALINID CILIATE IXFUSORIANS. 219 



cilia line interval, anterior 0.00162 nim., middle 0.00275 mm. pos- 

 terior 0.00275 mm. ' 



The long and abundant cilia differentiate this species from O. 

 ohtrigonoidea. The nuclei are of very diverse size in my infections 

 due probably to the fact that division is taking place rather fre- 

 quently, giving numerous small daughter nuclei and half-grown 

 nuclei. The full-sized nuclei are large. 



OPALINA HYLAXENA, form ORBICULATA, new forma. 



Type. — United States National Museum Cat. No. 16575. 



Host. — Eyla versicolor LeConte, many infections in tadpoles from 

 Woods Hole, Massachusetts, July 21, 1919, collected for Dr. E. C. 

 Just, who kindly gave them to me. All were found abundantly in- 

 fected, but none of three adults of this tree frog from the same 

 locality, which I opened, contained any Opalinas. 



Fig. 192. — Opalina htlaxena form orbiculata, X 117 diameters ; c and d indicati-: 



THE LONGITUDINAL RIDGES SEEN IN MANY INDIVIDUALS. 



Measurements. — Length of body 0.205 mm.; width of body 0.154 

 mm.; diameter of nuclei 0.00755 mm. to 0.0085 mm.; diameter of 

 nuclei of somewhat smaller individual 0.006 mm. to 0.0065 mm. 



This very broad and short Opalina has very large nuclei. The 

 animals are also quite thick. Most of the individuals are longi- 

 tudinally plicate, the ridges being very noticeable both in life and in 

 preserved specimens. I can not connect this form confidently with 

 any species. These may be actively growing infections of O. 

 hijlaxena, short and broad because of the frequency of transverse 

 division. The evidence pointing in this direction is the fact of resi- 

 dence in the same host and the further fact that the nuclei are 

 very large, as in O. hylaxena. It seems best, at least tentatively, 

 to class the Woods Hole forms as a forma or a possible subspecies of 

 O. hylaxena. 



OPALINA HYLAXENA, form PARVINUCLEATA, new forma. 



Type. — By some mistake no specimens of this forma were kept. 

 Endeavor will be made to obtain more material and, if successful, a 

 type slide will be deposited in the United States Nation nl Museum. 



