CHAPTER VI: THE ROCK-BORERS 



Family Saxicavid^ 

 Genus SAXICAVA, F. de B. 



Shell equivalve, thick, gaping at both ends ; hinge with single 

 cardinal tooth; ligament external, strong; animal symmetrical, 

 elongated; foot finger-like; mantle, cavity closed, all but pedal 

 opening; siphons large, long, covered with thick skin; orifices 

 fringed. A small number of living forms; many fossil. Borers 

 in sand, mud and soft rock. 



The ways of this rock-borer are worth studying, for the mol- 

 lusk is in the same class with the Teredo, as an undoer of man's 

 work. The boring it does in cement work, in breakwaters and 

 embankments, causes serious damage. The cells are large, often 

 six inches deep, and later comers bore through into cells already 

 completed, greatly weakening the structure. Each individual 

 attaches itself to the wall of its cell by a byssal cord, and thrusting 

 its siphons forth, settles down for life. The same cells are occu- 

 pied by successive generations; the young attach themselves 

 between the empty valves of parent shells. Thus several are 

 found nested together in one cell. 



The Arctic Rock-borer (S. Arctica, Linn.) is a representa- 

 tive of this family. It is found on cold New England coasts, 

 boring soft limestone, and living in the cavities. It often burrows 

 in mud or sand and affixes itself by a byssal cord to the root 

 anchors of large seaweeds. It occurs also on the Pacific coast 

 and in Northern Europe. It is largest in the coldest seas. Its 

 shell is oblong, angular, wrinkled and harsh, with toothed lamina- 

 tions, fit instruments for rock-boring. The form on our east coast 

 is less angular than the European, and larger. Length, J to 

 I J inches. Small forms occur on the Pacific coast. 



Genus PANOP.ffiA, Menard (GLYCIMERIS, Lam.) 



Shell oblong, thick, equivalve, gaping widely at both ends, 

 usually smooth, with epidermis; hinge near centre of dorsal 



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