24 AUGUSTA ÄRNBÅCK-CHRISTIE-LINDE, NORTHERN AND ARCTIC JNVERTEBRATES. 



mouth of the fjord. It has been observed that water coming from the North At- 

 lantic streams into this fjord in Spring. Many an animal, adult or as larva, is 

 supposed to have been brought there with that water from other regions. Thus 

 there is reason for the supposition that the occurrence of P. corrugata in Gullmarn 

 is due to the same fact. 



P. corrugata general ly occurs on sandy a bottom, sometimes on muddy bottoms 

 with stones. Depth down to 200 m. 



Ypsilocarpa clipeata 1 , gen. et sp. n. 



IM. 1, figs. 14—17. 



Habitat: 



N. W. Spilzbergen: Smeerenburg Bay, 25 fms, stones and clay, 1 sp, along 

 with Styela rustica (August 27, 1872, Spb. Exp. 1872—1873). 



Description. 



External Appearance. 



The body is ovoid and somewhat compressed baso-apically; the test is spread 

 out över the object to which the animal is attached. The apertures are situated 

 on the dorsal surface, about 2 l /2 mm. apart, and, in this preserved specimen, scarcely 

 raised över the surface, and not easily detected. They are surrounded by ele- 

 vations of the test, which are covered with numerous minute tubercles (Pl. 1, fig. 14). 

 The test of this preserved example is of a yellowish-grey colour and very firm. Its 

 surface is divided all över into irregular polygons. In the middle of each polygon 

 is a 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 of a somewhat smaller size, though more promi- 

 nent. 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 musculature is not very strongly developed. The tentacles 

 are simple and of differing size, the largest numbering about seven or eight. 



The atrial tentacles are numerous and slender; they are scattered över the 

 narrow velum and arranged in two or three rows. The dorsal lamina is plain- 



1 A preliminary note on this species lias been published in »the Annals and Magazine of Xatnral 

 Hi story», Ser. 9. Vol. 7. London 1921. 



