70 pectinidjE. 



consists of numerous fine ribs, which radiate from the beaks to 

 the front and side margins, and have their crests thickly set 

 with short vaulted spines or prickles ; besides these riblets, the 

 surface is closely covered with extremely minute and irregular 

 longitudinal striae, which are raised and divaricate or become 

 forked, but they are never reticulated or punctured as in 

 P. Tested. The .colour is of a more sombre hue. The left ear 

 of the upper valve hangs down much lower, and is nearly 

 entire instead of being deeply notched as in that species ; and 

 the byssal sinus is consequently larger. L. 0-725. B. 0*7. 



Habitat : Seas of Shetland, Scotland, north-eastern 

 coasts of England, north, east, south, and west of Ire- 

 land, Isle of Man, and Scilly, in 12-90 fathoms, hard 

 ground. Morch has procured it from the Faroe Isles, 

 and Danielssen from West Finmark. It also inhabits 

 other parts of the Scandinavian coast. M f Andrew has 

 dredged it in Vigo Bay at a depth of 15 fathoms, and 

 Philippi describes it as a Calabrian fossil under the 

 name of P. rhnulosus. 



The shell is sometimes distorted. The pallial ocelli or 

 eyelets are of unequal size and irregularly placed ; they 

 gleam with an opaline lustre. Living specimens which 

 I dredged in 85 fathoms had the shells highly coloured 

 and streaked. Mr. Norman has noticed, in his list of 

 Clyde Mollusca, that the shells of this species lose the 

 azure-blue colour after being kept in a closed cabinet. 

 This is remarkable, because certain colours of shells and 

 other animals {e.g. pink and reddish- brown) fade, and 

 even vanish, unless the light is excluded. In the British 

 Museum it has been found necessary to replace, every 

 two or three years, fresh specimens of many delicate- 

 tinted butterflies exposed in the show-cases; and in 

 the museum at Amsterdam the shells are always kept 

 covered to prevent loss of colour. P. striatus attains a 

 greater size than P. Testes. My largest specimen is about 



