34 CONCHYLIA— D/THFiJ^. 9. 



9. LYONSIA-Tl/J^rOiV. 



Testa transversa, incequivalvis, inoEquilateralis, latere antico hiante. 

 Cardo dente transversa cordato mohili communi, valvas foveolis trans- 

 versis coadunante : lateralibus nullis. Ligamentum internum. 



Shell transverse, inequivalve, inequilateral, open at the anterior end. 

 Hinge with a transverse heart-shaped moveable tooth, common to 

 both the valvesj and uniting them by a transverse cavity in each : 

 lateral teeth none. Ligaoicnt internal. 



This genus is remarkable for the peculiar structure of tl.e hinge, 

 which consists of a single tooth placed on the inside equally be- 

 tween the two valves, uniting them by a transverse ligament in each, 

 which is seated in a narrow and rather oblique cavity on the ante- 

 rior side. 



This tooth is not a fixed projection from either of the valves, nor 

 formed from the substance of the shell itself, as in all other known 

 shells furnished u ith teeth : but is an independent process, moveable 

 with the ligament, and may be entirely detached from either or both 

 the valves : consequently when the valves are opened, it is found 

 sometimes in the rii^ht valve and sometimes in the left, as the liga- 

 ment may casually loosen, e.xhibiting the form of a somewhat ele- 

 vated transverse tooth. 



It is of an oblong heart-shaped figure, appearing like a piece of 

 enamel fixed to >h j ohit of junction beiveen the valves, with the 

 pointed end direc.ly under the beaks. 



We have dedicated it to our worthy correspondent, Mr. Lyons of 

 Tenby, who i"rst presented it to the notice of the British naturalist 



