MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 305 



the foot short, oblong, flattened ; the tubes united, very 

 extensile ; the mouth small, with very small labial ap- 

 pendages ; the branchiae elongated, narrow, somewhat 

 unequal, united above nearly in their whole length, and 

 prolonged into the siphon. 



Shell subovate or oblong, equivalve, inequilateral, 

 generally thin and white, open at both ends, more 

 widely at the anterior ; the umbones concealed by a cal- 

 losity; the hinge toothless, and without ligament, but 

 usually furnished with several accessory calcareous 

 pieces ; a curved, flattened, calcareous process in each 

 valve, under the umbo ; muscular impressions distant, 

 submarginal, the posterior large and elongated ; pallia] 

 impression distinct, with a deep sinus behind. 



The species reside imbedded in rocks, wood, clay, and 

 other more or less firm substances ; and the genus taker 

 its name, as Pennant remarks, from <£aAeco, to sink in 

 cavities ; or from <pa>\as, residing in caves. 



It might be supposed that on a coast composed chiefly 

 of primary and igneous rocks, few or no boring Mol- 

 lusca could find a suitable place of abode ; but the follow- 

 ing extract from the Statistical Report of the Parish of 

 Belhelvie will shew that such an opinion would not be 

 correct : — " It is probable that this moss extends a con- 

 siderable depth out to sea, and that there is a submarine 

 forest somewhere in this bay at no great distance ; for 

 on Christmas 1799, when there was perhaps the most 

 dreadful tempest that any person remembered to have 

 seen on this part of the coast, several cubical blocks 

 of peat moss were cast by the sea upon the sandy beach, 

 some of them containing upwards of 1700 cubic feet. 

 Pieces of wood, like branches of oak trees, apparently 

 converted to a consistence like moss, passed through 

 these blocks in every direction. Both moss and wood 

 were perforated by a number of Auger worms of a large 

 size, and most of them alive in their holes." I have 

 also been informed that, many years ago, after a great 

 easterly storm, the beach at Aberdeen was covered with 

 a vast quantity of shells, among which were numberless 



& \j & 



