MANUAL OF NATUKAL HISTORY. 153 



10. Family. — Galeommas (Galeommidse). Mantle 



very large, double-edged, tubercled, almost 

 entirely open, with a single aperture at hind 

 part ; foot long, ligulate, perforate, byssifer- 

 ous ; shell thin, equivalve, transversely oval, 

 entire, ventral margin gaping ; hinge eden- 

 tulate ; ligament internal. 



1 1 . Family. — Pandoras (Pandoridse). Siphons 



short, united nearly to their ends, ends diver- 

 gent, fringed ; shell equivalve, pearly within ; 

 ligament internal, hinge often with an inter- 

 nal ossicle. 

 ] 2. Family. — Corbulas (Corbulidse). Siphons very 

 short, united, ends fringed, and with a mem- 

 branous tube ; mantle almost entirely open ; 

 foot narrow ; shell inequivalve, beaked an- 

 teriorly ; hinge with primary teeth in one 

 or both valves ; cartilage in an internal pit. 



13. Family. — Stone-Borers (Saxicavidse). Mantle 



closed except for passage of foot ; siphons 

 elongate, united ; foot byssiferous ; shell ir- 

 regular, gaping at ventral margin ; hinge 

 with a few primary teeth. 



14. Family. — Laseas (Laseidse). Mantle with only 



one (anal) opening, folded anteriorly into a 

 canal or tube ; foot ligulate, grooved, byssi- 

 ferous ; shell small, tumid or compressed ; 

 ligament and teeth variable. 



15. Family. — Scale-Shells (Leptonidse). Mantle- 



margin extending beyond the shell and cirr- 

 hated ; siphon short ; foot keeled and disked ; 



II 5 



