Observations on British Zoophytes. 315 
lumnar, with four tafts of thread-cells surrounding the 
mouth. 
A single specimen only of this interesting little Hydrac- 
tinia was obtained, parasitical on a dead shell of Natica 
Alderi brought in by the fishing-boats at CuUercoats. I 
have since seen a dead and rather worn specimen, upon 
Natica Groenlandica, among the Zoophytes collected in 
Shetland by the Rev. A. M. Norman. The species differs 
from H. echinata in its much smaller size, the simple linear 
form of its spines, their irregular grouping, and more espe- 
cially in its bearing medusoids ; these latter spring from 
the encrusting base. No capsule could be detected ; but this 
might possibly arise from its great transparency. The me- 
dusoids bear a great resemblance to those of Podocoryne 
carnea (Sars), the only difference being in their having eight 
intermediate tubercular tentacles. In this respect they also 
differ from the medusoid of a Hydroid polyp described by 
Professor Loven, and referred by him to Hydractinia, but 
which appears rather to belong to the genus Podocoryne^ 
as the base was not horny or spinous. As far as I am 
aware, therefore, this is the only instance in which medu- 
soids have been ascertained to be produced by a true Hy- 
dr actinia, 
2. Atmctylis arenosa, n. sp, PI. XIV. figs. 5-7. 
Polypary minute, consisting of a creeping fibre, from 
which arise short funnel-shaped tubes, rather irregular in 
form, but always expanding more or less at the top, from 
which the polyps issue, generally covered with minute 
grains of sand. Polyps entirely retractile, with long, 
slender, strongly muricated tentacles, varying in number, 
according to age, from six to twelve. 
The genus Atractylis has been established by Dr Strethill 
Wright for a group of Hydroid Zoophytes resembling Eu- 
dendrium in many of their characters, but differing in the 
conical form of the mouth of the polyp, and its retractility 
(partial or complete) within the tubular polypary. They 
are generally of small size, and seldom branched. Their 
reproduction is usually by medusoids ; but Dr Wright, who 
