transparent, and without the spur-like process on the left edge of
the carapace. The chief difference, however, lies in the number of
anal cirri. These are 10 in number and they are arranged obliquely as
in the preceding species, with the largest one on the right and the
smallest on the left. The ventral cirri are 8 in number, and are
arranged in two rows, one of which, the right, has 4 cirri closely
arranged, the other having 3 cirri close together and one at some
distance, near the largest anal cirrus. The peristome, contractile
vacuole, and nucleus are similar to the preceding. Length 36µ; width
22µ.


[Illustration: Fig. 57.--_Aspidisca polystyla_.]


Stein assigns only 7 ventral cirri to this species, but he also
describes 2 very fine bristle like cilia (p. 125) and pictures them
in figs. 18, 19, 20, and 21 of his Taf. III in the same relative
position as my eighth cirrus. I am positive that cilia do not occur
on the ventral face of this form, and that the characteristic cirri
are the sole locomotor organs.


KEY TO FAMILIES OF PERITRICHIDA.

a. Peristome drawn out into Family _Spirochonidæ_
funnel-like process; parasitic

b. Adoral zone and circlet of cilia Family _Lichnophoridæ_
at opposite end. Adoral zone (one genus, *_Lichnophora_)