MALLEUS 



TESTA irregularis^ subaequivalvis, bysso adhaerens^ 

 elongata^ basi plerumque lobis lateralibus duobus. 

 Umbones divaricati. Cardo edentulus. Liga- 

 mentum externum^ areae trigoni obliquae in utra- 

 que valva^ fossula centrali, obliqua, elongata^ 

 affixum/ Sinus hyssi in valva inferiore pone 

 cardinem positus. Impressiones musculares in 

 utraque valva duae, altera magna^ subreniformis^ 

 lateralis ; altera minutissima, infra cardinem 

 posita. 



Few Genera are so well characterized as Malleus; the 

 species which compose it were placed by Linne among the 

 Ostrece, with which indeed they agree perfectly well in the 

 structure of the external foliaceous portion of their shells, 

 but from which they may nevertheless be easily distinguished 

 by the mode of their attachment, which in Malleus is by a 

 byssus passing through a sinus behind the hinge in the 

 lower valve ; as the shell increases, this sinus is covered 

 over, in some species, with shelly matter, so that the byssus 

 then passes through a small aperture in the lower valve, 

 near to and behind the hinge ; sometimes also there is a 

 small sinus in a corresponding situation in the upper valve, 

 forming with that in the lower valve (when both valves 

 are closed), a small aperture through which the byssus 

 passes. There is only one other Genus with which this 

 can be confounded, the Pedum, of which we have already 

 mentioned the distinguishing Character. 



Shell irregular, nearly equivalve, elongated, its base 

 frequently furnished with two, sometimes much elongated, 

 lateral lobes, one on each side ; sometimes there is only 

 one of these, and some species have none at all, so that the 

 name of Malleus or Hammer Oyster, is not happily appli- 

 cable to all the species of the Genus, though particularly 



