3o6 MANUAL OF ZOOLOGY. 



Two subdivisions are comprised in this section. In the 

 first the siphons are short, and the pallial line is simple {Integro- 

 pallialia) ; as is seen in the families ChamidcB, Hippuritidce, 

 Tridamidce, Cardiadce, Lticinidce, Cydadidm, and Cyprinidos, 



The second subdivision {Simt-pallialia) is distinguished by 

 the possession of long respiratory siphons, and a sinuated pallial 

 line, and it comprises the famiUes Venerida, Madridce, Tellinidce, 

 SolenidcB, Myacidce, Anatinidce, Gastrochcenidce, and Pholadidcs. 



Synopsis of the Families of the Lamellibranchiata. 



Section A. Asiphonida. 



Fam. I. Ostreidce. — Shell inequivalve, slightly inequilateral, free or 

 attached ; hinge usually edentulous. Ligament internal. Lobes 

 of the mantle entirely separated ; the foot small and byssiferous, 

 or wanting. A single adductor. 111. Gen. Ostrea, Pecten, 

 Spondylus, &=(. 



Fam. 2. Aviculida. — Shell inequivalve, very oblique, attached by 

 a byssus ; hinge nearly, or quite, edentulous. Mantle-lobes free ; 

 anterior adductor small, leaving its impression within the umbo ; 

 posterior adductor large and sub-central. Foot small. 111. Gen. 

 Avicula., Inoceramus, Pinna, 



Fam. 3. Mytilida. — Sliell equivalve, umbones anterior, hinge eden- »• 

 tulous ; anterior muscular impression small, posterior large. 

 Shell attached by a byssus. Mantle-lobes united between the 

 siphonal apertures. Foot cylindrical, grooved, and byssiferous. 

 111. Gen. Mytitus, Modiola, Dreissma. 



Fam. 4. Arcades. — Shell equivalve ; hinge long, with many comb- 

 like equal teeth. Muscular impressions nearly equal. Mantle- 

 lobes separated ; foot large, bent, and deeply grooved. 111. Gen. 

 Area, Pectiineulus, Cuctillaa. 



Fam. 5. Trigoniada. — Shell equivalve trigonal ; hinge-teeth few, 

 diverging ; umbones directed posteriorly. Mantle open ; foot 

 long and bent. 111. Gen. Trigonia, Axinus. 



Fam. 6. Unionidie. — Shell usually equivalve, with a large external 

 ligament. Anterior hinge-teeth thick and striated ; posterior 

 laminar, or wanting. Mantle-lobes united between the siphonal 

 apertures. Foot very large, compressed, byssiferous in the fry, 

 111. Gen. Unio, Anodon, Mulleria, 



Section B. Siphonida. 



Subdivision I. Integro-pallialia. — Siphons short, pallial line simple. 



Fam. 7. C/iamidte. — Shell inequivalve, attached; hinge-teeth 2-1 

 (two in one valve and one in the other). Adductor impressions 

 large. Mantle closed ; pedal and siphonal orifices small and 

 nearly equal. Foot very small. 111. Gen. Chama, Dicei-as. 



Fam. 8. HippuritidtB. — " Shell inequivalve, unsymmetrical, thick, 

 attached by the right umbo ; umbones frequently camerated ; 

 structure and sculpturing of valves dissimilar ; ligament internal ; 

 hinge-teeth 1-2 ; adductor impressions 2, large, those of the left 

 valve on prominent .".pophyses ; pallial line simple, sub-marginal." 

 — (Woodward.) 111. Gen. Hippitrilcs, Kadiolites, CaprincUa. 



