Styelid Tunicate from Spitzbergen. _ 349 
The test of this preserved example is of a yellowish-grey 
colour and very firm. Its surface is divided all over into 
irregular polygons ; this striking character clearly distin- 
guishes the species from other Arctic Styelids. In the middle 
of each polygon isa minute, translucent, vesicle-like elevation. 
On larger polygons there are two such structures, and here 
and there, especially in the vicinity of the siphons, they are 
more closely scattered, and are there of a somewhat smaller 
size, though more prominent (text-fig. 1). 
The surface is free from adherent foreign material. 
The specimen measures 6 mm. in length (baso-apical) and 
8 mm. in breadth (dorso-ventral). 
Internal Structure. 
The test is moderately thick and of a tough consistency. 
Its outer layer consists apparently of a very thin transparent 
membrane of a chitin-like aspect and of somewhat greater 
thickness around the vesicle-shaped elevations on the polygons. 
‘The inner surface of the test is smooth and whitish. 
The mantle adheres to the inner side of the test and the 
mantle musculature is not very strongly developed. 
The tentacles are simple and of differing size, the largest 
numbering about seven or eight. 
Atrial tentacles are present; they are numerous and 
slender, thickly scattered over the narrow velum. 
The dorsal lamina is plain-edged and rather broad. 
The dorsal tubercle is rounded and small, though prominent. 
The aperture is elongate and feebly curved (text-fig. 2). 
The branchial sac is of a characteristic structure. It is 
provided with three weil-developed folds on each side with 
wide longitudinal vessels ; the second fold is in a rudi- 
mentary state, and is represented by three longitudinal 
vessels, a number which is reduced to two in the bottom of 
the branchial sac. 
On the interspaces between the folds there is one wide 
longitudinal vessel. 
The following scheme shows the approximate number and 
the distribution of the vessels :— 
Dorsal lamina, 1 (9) 1(8) 1(7) 1(5) 1, endostyle. 
The stigmata are elongated and of the usual form. 
The alimentary canal is not of great length. The stomach 
is short and has a horizontal position. Numerous longi- 
