Observations on British Zoophytes. 



315 



lumnar, with four tufts 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 Cullercoats. I 

 have since seen a dead and rather worn specimen, upon 

 Natica Groenlandica, among the Zoophytes collected in 

 Shetland by the Bev. A. M. Norman. The species differs 

 from H. ecliinata 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 

 camea (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. Atractylis 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 



