The Piddocks 



mollusk grinds or scrapes its way into the stiffest clay, its fa- 

 vourite burrow. It is two to four inches long. It is found in 

 California, New England and Europe. 



Genus PHOLADIDEA, Turt. 



Shell globose-oblong, with cross furrow, anterior gape large, 

 closed, when mollusk is full grown, with callous plate; accessory 

 plates minute. Animal with fringed disk at tip of siphons, and 

 horny cup at their base. 



The Paper Piddock (P. papyracea, Sol.) of Europe is the 

 type. Thin as paper, yet it burrows into sandstone, hard clay, 

 peat and buried wood along the Irish and Channel coasts. The 

 basal cup seems to be a shield for the retracted siphon. 



P. penita, Conr., occurs in soft rocks on the California 

 and Oregon coasts. Its back is broad, the umbones covered 

 with a round shield, in front of which lie the dorsal plates 

 side by side. Two fin-like appendages proceed from and protect 

 the base of the siphons. It is described as excellent eating. 

 Length, 2 inches. 



Some pholads burrow into oyster shells, some in hard timber, 

 one in floating cakes of wax on the Cuban coast; an Australian 

 species is found in resin; a fossil species resembles Teredo in lining 

 its burrow with shell. A fresh water species works in wood sev- 

 eral miles above the mouth of a Bornean river. 



Genus XYLOPHAGA, Turt. 



Shell globular, with cross furrows; gapes in front; is closed 

 behind; burrow oval, with shelly lining; animal withdraws within 

 shell, except siphons; foot thick, extensible. 



The Wood Piddock {X. dorsalis, Turt.) of Europe and 

 America, is a little nut-like mollusk, boring wood to the depth 

 of an inch, and apparently eating the sawdust it makes. It 

 always works across the grain. The boring instrument is the 

 long elastic foot. The shell is covered with epidermis. Length, 

 I inch. 



This wood borer is in a sense a connecting link between 

 Pholas and Teredo, at least as far as choice of material for bur- 

 rowing goes. 



Habitat. — North Atlantic Ocean. 



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