150 MANUAL OF NATURAL HISTORY. 



an epidermis ; ligament external ; hinge with 

 cardinal and lateral teeth. Fluviatile. 



7. FAMILY. Paphians (Paphiidse). Shell variable 



in form ; ligament internal ; pallial impres- 

 sion sinuated ; hinge with the anterior car- 

 dinal tooth simple, compressed. 



8. FAMILY. Madras (Mactridse). Siphons united 



to their extremities, which are fringed ; foot 

 linguiform, geniculate ; shell with the carti- 

 lage internal ; two cardinal teeth in each 

 valve, the anterior usually bifid. 



9. FAMILY. Anatinellas (Anatinellidse). Shell 



oblong, rather gaping behind, equivalve, 

 covered with an epidermis ; cartilage internal, 

 in a pit ; lateral teeth none ; siphonal inflec- 

 tion none. 



10. FAMILY. Tellens (Tellinidse). Siphons long, 



slender, entirely separate ; foot broad, geni- 

 culate ; shell regular ; hinge with two primary 

 teeth in each valve ; ligament external ; si- 

 phonal inflection deep. 



11. FAMILY. Mud- Madras (Scrobiculariidse). Ori- 



fices of siphonal tubes plain j mantle-margin 

 toothed ; foot large, compressed ; shell slightly 

 gaping posteriorly ; hinge with an internal 

 cartilage situated in a pit. 



12. FAMILY. Wedge-Shells (Donacidse). Mantle 



freely open in front ; siphons separated to 

 their bases ; foot large, sharp-edged, with a 

 byssal groove ; shell variable in form, more or 

 less wedge-shaped ; hinge with primary teeth. 



