36 Lamarck's Genera of Shells. 



3. Malleus*. 



Shell subequivalve, rude, deformed, generally elongated, sub- 

 lobate at the base ; beaks small, diverging. Hinge without 

 teeth. An elongated, conical pit, below the beaks, obliquely 

 traversing the facet of the ligament. Ligament subexternal, 

 short, inserted in the short, sloping facet of each valve. 



The mallei are distinguished from the pernss by their hinge; 

 from the aviculae by the conical pit below the beaks, and by 

 the valves being, though irregular, of the same size, and having 

 no sinus on the left valve. The mallei are remarkable for their 

 form ; they are coarse, irregular shells, with little beauty exter- 

 nally. Internally they are rather brilliant pearly, especially at 

 the part occupied by the body of the animal. They are exotic 

 sea shells, and some of the species (as the malleus albus) very 

 rare. They have a byssus, which protrudes through a small 

 posterior aperture, near the beaks. The inclined sides of the 

 valves form an open channel at the base. 



Type. Malleus albus t. 

 Shell trilobate ; lateral lobes of the base very long ; no sinus 

 for the byssus, or not distinct from the pit of the ligament. 

 South-oriental seas. 6 Species. PI. I. Fig. 83. 



4. Avicula I. 



Shell inequivalve, brittle, rather smooth ; base transverse, 

 straight ; extremities produced, the exterior caudate. A sinus 

 in the left valve for the passage of the byssus. Hinge linear, 

 unidentate ; cardinal tooth of each valve under the beaks. 

 Facet of the ligament, marginal, narrow, channelled, not tra- 

 versed by the byssus. 



When the valves are spread open, without separating, the 

 shell has a rude resemblance to a bird on the wing, whence its 

 name. 



The aviculae are sea shells, generally muticate, or not squa- 

 mose externally, thin, and pearly within. Their beaks are ob- 

 lique, small, and not prominent. 



* A hammer. t White. J A littk bird. 



