22 COl^CnyUX—DfTHYRA. 4. 



Shell nearly an inch long, and an inch and a half broad, white 

 covered with a yellowish brown skin, regularly striate transversely, 

 witii one of the valves generally much more tumid than the other : 

 beaks nearer the middle than in the last species. 



This species is subject to mucli variation of figure, being fre- 

 quently nearly globular, but always rounded and soniewiiat open 

 at the ends. Sometimes it is found attached to clefts in the rocks, 

 but not imbedded in them, when there is a considerable opening 

 in the front margin for the issue of the byssus of attachment. 



It was observed in great abundance, in Melville Island, in the 

 Polar regions, three miles distant from the shore, where it had 

 probably been cast by the agitation of the sea, and when deprived 

 of the inhabitant driven inwards by the violence of the w inds, by 

 Mr. Griffiths, an officer in Capt. Parry's late northern expedition. 

 The specimens we examined, in no respect differed from our 

 native ones, being regularly striate transversely, with both tlie 

 extremities rounded and a little gaping: but they were larger. 



piicaia. Saxicava testu ohlongd, latere antico dilatato hiante, lamellis 

 transversis. 

 Shell oblong, dilated and open at the anterior end, and trans- 

 versely laminar. 

 Mytilusplicatus. Chemnitz, viii. p. 153, tab. 82, fig. 733. 

 Gmelin, Syst. p. 3358. 

 Pennant, Brit. Zool. iv. p. 242. 

 Turfon, Linn. Syst. iv. p. 295. 

 Montagu, Test. Brit. Suppl. p. 70. 

 Dillwyn, Descript. Catal. p. 306. 

 Twr^on, Conch. Diet. p. 114. 



