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396
D ’A it c r w.
THOMPSON, HYDROIDA.
Thuiaria turgida, S. F. Clarke.
Pl. 17, fig. 14 and 15.
This Alaskan species, whieh was one of the most abundant
in Clarke’s collection, is represented in the Vega collection
by a single example from 42° 36’ E. long.
T. turgida is a very distinet species, conspicuous for its
stout habit, and close, thick-set, opposite hydrothecse. The
latter measure 0,5 mm. in length. It belongs to the same
division of the genus as T. articulata, resembling it in its regular
pinnate habit, and the plaiti circular orifice of the hydrotheca.
No natural size drawings of this or the following species
of Thuiaria have yet been published, and I accordingly present
figures of them ali.
The three following species of Thuiaria are closely allied.
They belong to the group of plumose species with bilabiate
hydrothecse’, which seem to be especially abundant in the
Alaskan region. There the group is represented by T. robusta,
S. F. C., T. plumosa, S. F. C., and by T. (Sertularia) cupressoides,
and similis, S. F. C.1 Our T. (S.) cupressina and argentea,
All-man^ T. ramosissima (which must be very similar indeed to
T. plumosa), from N. E. America (Journ. Linn. Soc., 1885, p.
146). and T. Vegce, n. sp., from the present collection, are the
remaining forms ascribable to the group.
Thuiaria plumosa, S. F. Clarke.
Pl. 18, fig. 16. Pl. 21, fig. 26 and 27.
The Vega collection contains specimens of this species
from the station in long. 174° 27’ E.
It is a large and handsome species, the older specimens
having their upper branches thinned away, and tapering
up-wards to a pointed apex, much as in old specimens of T. (S.)
cupressina. But the branches are longer, and the hydrothecse
larger than in the latter species, and the extensive space of
bare stem in the lower portion of the zoophyte is a feature
not shared by the other. An exaggeration of the same feature,
combined with a stiffer but at bottom quite similar mode of
branching, would lead us directly to the peculiar habit of
T. thuja.
1 These species, ascribed by Clarke to Sertularia, are, as Allman has
remarked of S. cupressina and argentea, true Thuiarije. (Journ. Linn. Soc.,
187-5, XII, p. 267.)
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