Polyzoa of Queen Charlotte Islands. 213 
low), surrounded by raised lines, surface thickly covered with 
punctures ; orifice expanded above and well arched, contracted 
below ; peristome slightly raised, especially above, a very 
prominent hinge-denticle on each side a little above the lower 
margin ; immediately below it an umbonate swelling, bearing 
on its inner aspect an aviculardum, with rounded mandible, 
directed upwards. Occiwm rounded, not prominent, surface 
somewhat roughened, usually a circular pore on the front. 
Zoartum white and silvery. 
Houston-Stewart Channel, on shell. 
Mucronella spinosissima, Hincks. 
On further examination I find that in the younger cells there 
are two or three lines of pores forming a belt round the mar- 
gin; and it seems probable that the curious tubular system 
which I have described (‘ Annals’ for January 1884, p. 53) 
owes its origin tothese. Atleast I can only explain it by sup- 
posing that, as calcification proceeds, it is arrested by the 
pores, and only extends round them and not over them ; so 
that they continue open, and form at last tubular shafts piercing 
the stony crust which has been piled up about them. 
Retepora Wallichiana, Hincks. 
This species has been obtained in Vancouver Island. 
General Remarks. 
The number of species recorded in the present Report from 
the Queen Charlotte Islands is 96, of which 36 appear to 
have been hitherto undescribed. Of the 60 species known to 
science more than a third (24 at least) seem to be distinctively 
Arctic forms, and of these 17 occur in the British seas *. 
Migration has taken place on the side of Davis Straits and 
Behring Straits: on the one the circumpolar species have 
distributed themselves along the North-American coasts and 
more or less widely along those of the British Islands; on 
the other they have colonized the nearer portions at least of 
the North Pacific. In the comparatively warm waters which 
* The seven Arctic species which occur in the Queen Charlotte Islands 
but not in Britain are Cellaria borealis, Flustra membranaceo-truncata, 
Membranipora S phie, Smittia plicata, Retepora Wallichiana, Cellepora 
incrassata, and Myriozoum coarctatum. The whole number of species 
common to the Islands and Britain is forty-three. . 
