320 MANUAL OF THE MOLLUSCA. 



SAXICAVA, Bellevue. 



Etym. Sazum* stone, cavo, to excavate, S. rugosa, PI. XXII. fig. 13. 



Syn. Byssomya, Cuv. Rhomboides, Bl. Hiatella (minuta) Daud. 

 Biapholius, Leach. Arcinella (carinata) Phil. 



Shell when young symmetrical, with 2 minute teeth in each valve ; adult 

 rugose, toothless ; oblong, equivalve, gaping, ligament external ; pallial line 

 sinuated, not continuous. 



Animal with mantle-lobes united and thickened in fro at ; siphons large, 

 united nearly to their ends, orifices fringed ; pedal opening small, foot finger- 

 like, with a byssal groove ; palpi small, free ; gills narrow, unequal, united 

 behind and prolonged into the branchial siphon. 



Five genera and 15 species have been manufactured out of varieties and 

 conditions of this Protean shell. It is found in crevices of rocks and corals, 

 and amongst the roots of sea-weed, or burrowing in limestone and shells ; at 

 Harwich it bores in the cement stone (clay iron-stone), at Folkestone in the 

 Kentish-rag, and the Portland stone employed in the Plymouth Breakwater 

 has been much wasted by it. Its crypts are sometimes 6 inches deep (Couch] ; 

 they are not quite symmetrical, and like those of the Lithodomus are in- 

 clined at various angles, so as to invade one another, the last comers cutting 

 quite through their neighbours ; they are usually fixed by the byssus to a 

 small projection from the side of the cell. The Saxicava ranges from low- 

 water to 140 fathoms ; it is found in the Arctic Seas, where it attains its 

 largest size ; in the Medit, at the Canaries, and the Cape. It occurs fossil 

 in the Miocene tertiary of Europe and in the U. States, and in all the 

 Glacial deposits. 



GLYCIMERIS, Lamarck. 



Etym. Glukus, sweet, meris, bit. 



Type, G. siliqua, PL XXII. fig. 14. Syn. Cyrtodaria, Daud. 



Shell oblong, gaping at each end ; posterior side shortest ; ligament large 

 and prominent; epidermis black, extending beyond the margins; anterior 

 muscular scar long, pallial impression irregular, slightly sinuated. 



Animal larger than its shell, sub-cylindrical; mantle closed, siphon 

 united, protected by a thick envelope ; orifices small ; pedal opening small 

 anterior ; foot conical ; palpi large, striated inside, the posterior border plain ; 

 gills large, extending into branchial siphon. 



Distr. Arctic Seas, Cape Parry, N. W. America. Newfoundland. 



Fossil, Miocene . Brit. Belgium. 



FAMILY XIX. ANATINIDJD. 



Shell often inequi valve, thin ; interior nacreous ; surface granular ; liga- 

 ment external, thin; cartilage internal, placed in corresponding pits and' 



