Dr. J. E. Gray on some Families of Bivalve Shells. 415 



7. Corbulida,Syn.B.'SLlS42,78; P. Z.^. 184.7,192. Siphons 

 moderate. Foot small. Gills two on each side, dependent, 

 separate, moderately prolonged ; lips long. Shell porcellanous. 

 Hinge with a conical tooth and a cartilage-pit on each valve. 



8. Pandorida, Syn. B. M. 1842, 78; P. Z. S. 1847, 192. 

 Siphons large. Foot moderate. Gills subpinnate, one on each 

 side, greatly prolonged ; lips long. Shell pearly. Hinge with 

 two diverging teeth and a triangular pit on each valve. Valves 

 very unequal. 



Subclass 2. Asiphonophora. Mantle lohes mostly free, bearded 

 behind or on the whole edge, sometimes with a separate siphonal 

 opening for the vent. 



Order III. Lasiacea. 



Mantle lobes united, with an anal aperture under the hinder 

 adductor muscle, and a pedal aperture. 



1. Solenomyada, Syn. B. M. 1842, 78 j P. Z. S. 1847, 192. 

 Pedal opening anterior. Foot large, oblong, clavate, truncated 

 at the end. Siphonal opening in a disc, surrounded with long 

 beards. Gills pinnate, appearing only one on each side, broad, 

 of separate threads. Palpi small, slender. Shell gaping, thin. 

 Periostraca hard, polished, dilated beyond the shell; cartilage 

 internal. Animal, leaps and s\vims about by suddenly drawing in 

 the umbrella-shaped foot, at the same time the water is expressed 

 from the hinder opening by the closing of the valves. 



2. Lasiadce, Syn. B. M. 1&42, 78; P. Z. S. 1847, 192. Pedal 

 opening inferioi*, moderate, front edge sometimes produced into 

 a hood (or united and forming an anterior aperture for an in- 

 halant siphon ?) . Gills two, laminar, dependent, unequal, oblong, 

 on each side ; hps cylindrical, outer pair small, inner very broad. 

 Foot compressed, ^dth a central inferior groove, byssifei'ous. 

 Mantle double-edged, inner dilatile. 



Order IV. Unionacea. 



Mantle lobes free, slightly united behind, forming a separate 

 anal siphonal opening placed under the hinder adductor muscle. 



Suborder 1. Lucinacea. Foot cylindrical, elongate, inferior; 

 anterior adductor muscle generally elongate. 



1. Lucinida, Syn. B. M. 1842, 80; P. Z. S. 1847, 195. 

 Anal siphons elongate, cylindrical, retractile into the mantle- 

 cavity. Pedal opening inferior, moderate. Gills lamellar, only 

 one on each side the bodv, oblong, broad, united behind the base 



