16 McMURRICH. [Vot. III. 
with opaque white. The tentacles and disc are brown, also 
flecked with opaque white; and the peristome is white. 
The base is firmly adherent and somewhat larger than’ the 
column. The latter measures from 0.5-I cm. in height and from 
0.3-0.4 cm. in diameter, and is provided with a single row of cin- 
clides situated on tubercles, and six in number. They are color- 
less and transparent, so that they are quite conspicuous. No 
trace of a sphincter muscle could be seen ; and as in the forms 
already described, the “yellow cells’’ were abundant in the 
endoderm. 
The tentacles are entacmzeous, and in four cycles, their 
formula being 6, 6, 12, 24. The length of those of the inner 
cycle is about 0.4 cm. 
The mesenteries are arranged in three cycles. Of these, the 
first is perfect ; the second, imperfect and small, and not provided 
with mesenterial filaments; while the third is represented by 
the merest rudiments of processes from the mesogloea of the 
column wall. In one specimen examined there was a difference 
in the mesenteries of the two halves of the body. In one half 
there were three perfect pairs of mesenteries, and in the other, 
four, the secondary and tertiary cycles being arranged corre- 
spondingly. I could not discover the mesenterial stomata, nor 
a parieto-basilar muscle. The longitudinal muscle bands of the 
perfect mesenteries cover only a comparatively small portion of 
the surface of the mesentery, and end abruptly internally, as in 
variety £. 
In none of the specimens examined were there any traces of 
reproductive organs, as might be expected from the slight devel- 
opment of the mesenteries of the second and third cycles. 
My reasons for at first supposing this form to be a distinct 
species were its occurrence in such large numbers, all being 
about the same size, and the failure to obtain any larger speci- 
mens, resembling varieties a or 8, from the lake. A careful 
examination of the shores and deeper portions of the lake was 
not made; and it is probable that adult specimens of variety B 
may be found there, in the deeper water, a little way out from 
the shore, the shallower water and the grass abounding there, 
with the myriads of copepods swimming about among it, afford- 
ing more suitable conditions for the growth of the young forms. 
There can be no doubt but that the specimens are young, and 
