60 
longer radial shields, different upper arm plates and more pent¬ 
agonal oral shields; also the tentacle scale of the side arm plate 
is bigger. Further the number of armspines is different; the young 
specimen of 6 mm of arcystaia (which is somewhat larger than 
the type of A. Griegi) „rarely has 6 armspines, and usually there 
are but 4; these are more siender, more diverging and longer than 
in the specimen of A. Griegi“. 
Judging from the single specimen of A. Griegi in hånd there 
can thus be no doubt that it is really a distinet species, though 
nearly related to arcystata. The latter species being known only 
from off the Californian coast and from the Japanese Seas it is, 
of course, not very probable either that the Scandinavian form 
should be identical with it. 
7. Ophiactis nidarosiensis n. sp. (Fig. 5). 
Diameter of disk ca. 2.5 mm; arms 12—15 mm long. Disk 
covered with rather coarse scales, sparsely set with short spines. 
Primary plates not distinet. Radial shields about half the length of 
radius of the disk, separated throughout by a linear series of 2—3 
scales. The ventral side of the disk covered with a more delicate 
scaling, generally without spines. Arms 6, sometimes 5, very rarely 
Fig. 5. Ophiactis nidarosiensis. ~ 
a. ventral side. b. dorsal side. 18 /i. 
7; the dorsal plates are rather 
broadly in contact in the inner 
part of the arm, with a trunc- 
ate inner end and the outer 
edge forming a high arch; 
they are sligthly longer than 
broad. Ventral armplates dis- 
tinctly longer than broad, with 
a narrow, truncated inner apex; 
the first ventral plate is com- 
paratively large, longer than 
broad, the second is about as 
broad as long. One rounded 
tentacle scale. The sideplates 
are rather prominent, carrying 
four, farther out three spines. 
On fullgrown arms the upper 
