42 Rev. T. Hincks otr the 



? Porella argentea, n. sp. (PL IX. fig. 1.) 

 Zocecia ovate, quincuncial, rather depressed (sutures shal- 

 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 avicularium^ with rounded mandible, 

 directed upwards. Ocecium rounded, not prominent, surface 

 somewhat roughened, usually a circular pore on the front. 

 Zoarium white and silvery. 



Houston-Stewart Channel, on shell. 



Mucronella spinosissima, Hincks. 

 On further examination I find tliat 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 (see page 27 of the Report) owes 

 its origin to these. At least I can only explain it by sup- 

 posing that, as calcification proceeds, it is arrested by the 

 pores, and extends around them but 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. 



Retep07'a Wallichianaj Hincks. 

 This species has been obtained in Vancouver Island. 



General Remarhs. 



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 whicli occur in the Queen Charlotte Islands 

 hut not in Britain are Cellaria boreah's, Fhistra membraiiaceo-tnmcata, 

 Memhranipora 8 phice, Smittia plkatn, Rdepora Wallichiana, Cellepora 

 incrassata, and Myriozoum coaj-ctatum. The whole number of species 

 conniion to the Islands and Britain is fortv-three. 



