TECTURA. 247 



Shell depressed, rather thin, opaque, and devoid of lustre : 

 sculpture, numerous very fine and sharp longitudinal striaB, 

 which radiate from the beak ; they are not visible by the naked 

 eye ; the surface is also covered with close-set and almost mi- 

 croscopical concentric strias, varied by occasional lines of 

 growth that are more conspicuous : colour greyish with dark 

 reddish-brown longitudinal streaks, which often are confluent 

 and forked, giving a tessellated or clouded appearance like that 

 of tortoiseshell ; sometimes the colour is reddish-brown varied 

 by broad rays or spots of white: heah rather sharp, placed 

 usually about one-third nearer the anterior end: wiowf/i roundish- 

 oval : margin expanded, even and smooth : inside shining and 

 polished, except at the margin, chocolate-colour in the centre 

 or dorsal scar, porcelain-white and highly glazed in the 

 middle, and of a dull hue at the margin, which is rather 

 broad and bevelled to a sharp edge. L. 0*85. B. 0*7. 



Habitat : On the under side of stones, at low water 

 and as deep as 20 f. in the laminarian zone, Shetland 

 Isles (Barlee); Orkneys (M^ Andrew and Thomas); 

 Caithness (Peach); Sutherlandshire (J. G. J.); Aber- 

 deenshire (Macgillivray) ; Moray Firth (Gordon and 

 others); west of Scotland (Brown and others); Belfast 

 (Hpidman) ; Lough Strangford (Dickie); Bangor, co. 

 Down (Clealand); Dublin Bay (Lloyd and others); Isle 

 of Man (Forbes); Berwick Bay (Howse) ; Northumber- 

 land and Durham, as far south as Hartlepool (Hancock 

 and others), and living in 40 f. (Alder). It is also 

 common and widely distributed throughout the Arctic 

 and North Seas from Greenland to Iceland, and from 

 Nova Zembla to the South of Sweden, as well as 

 Canada and the north-eastern coasts of the United 

 States. 



Forbes noticed the migratory habit of this remarkable 

 species, in his account of a shell-bank in the Irish Sea ; 

 and the Tyneside Naturalists^ Field-Club have given 

 some curious details of its southward march. Speci- 

 mens collected by Captain Bedford at Oban are nearly 



