320 MANUAL OP THE MOLLUSCA. I 



Saxicava, Bellevue. I 

 Ebjm. Saxum, stone, cavOf to excavate. S. rugosa, Pi. XXII. fig. 13, 

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

 Biapholius, Leach. Arcinella (carinata) Pliil. 



Shell vrben young symmetrical, viith 2 minute teeth in eacli valve ; adult ' 



rugose, toothless ; oblong, equivalve, gaping, ligament external ; pallid line j 



sinuatcd, not continuous. : 



Animal with mantle-lobes united and thickened in front ; siphons large, j 



united neai'ly to their ends, orifices fringed ; pedal opening small, foot finger- | 



like, \nth a byssal groove ; palpi small, free ; gills narrow, unequal, united I 

 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 cre\aces 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 i 



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 ai-e not quite symmetrical, and like those of the Lithodomtis are in- ! 



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



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- j 

 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 occm's fossil ; 



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



Glacial deposits. j 

 Glycimeris, Lamarck. 



Etym. Glukus, sweet, meris, bit. ; 



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



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



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



muscular scar long, pallial impression irregular, slightly sinuated. ! 



Aninial larger than its shell, sub-cylindrical ; mantle closed, siphons | 



united, protected by a thick envelope ; orifices small ; pedal opening small 1 



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. i 



Fossil, Bliocene — . Brit. Belgium. ,j 



I 



FAMILY XIX. Anatinid^. | 



Shell often inequivalve, thin ; interior nacreous ; sm-face granular ; liga- 

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



i 



