154? MANUAL OF NATUKAL HISTORY. 



shell orbicular, compressed, gaping at the 

 sides ; pallial impression simple. 



III. ORDER. GONIOPODS (Goniopoda). 



Foot angular, more or less compressed ; siphons 

 none or rudimentary ; mantle-lobes more or 

 less united. 



1. FAMILY. False-Cockles (Carditidse). Lobes of 



mantle disunited in their entire length, with 

 a single posterior opening ; foot compressed, 

 with a byssal groove ; shell closed, regular, 

 free ; hinge with one or two oblique cardinal 

 teeth, lateral teeth none. 



2. FAMILY. Chamas (Chamidse). Two short si- 



phons beset with cirrhi; lobes of mantle 

 united behind ; foot small, cylindrical, trun- 

 cate ; shell irregular, porcellanous, attached, 

 inequivalve, with a single large hinge-tooth ; 

 pallial impression not sinuated. 



3. FAMILY. Cockles (Cardiidse). Siphons short, 



their bases beset with cirrhi, margins fringed ; 

 foot large and geniculate ; shell cordate, with 

 radiating ribs and furrows ; hinge usually 

 with two primary teeth in each valve, and 

 distinct lateral teeth ; pallial impression not 

 sinuated. 



4. FAMILY. Heart- Cockles (Glossidse). Mantle- 



lobes united behind, with two short siphons ; 

 foot small, sub-angular, compressed, and 

 trenchant ; shell symmetrical, heart-shaped, 

 ventricose ; beaks spirally inrolled ; hinge 



