38 Lamarck's Genera of Shells. 



They are generally auriculated at the base or extremity of the 

 cardinal margin. They are all inequivalve, for, though in many 

 the valves are of the same size, one of them is always more 

 convex than the other. 



1st. Family. 



Pectinid.\. (7 Genera.) 



Ligament internal, or semi-internal. Shell generally regular, 

 compact, not foliated. 



The pectinida are usually auriculated, and striated ; the 

 striee, or ribs, radiating from the beaks. The ligament is internal, 

 but sometimes visible on the outside, in consequence of an in- 

 dentation between the beaks, or of their distance from one 

 another. Some are free shells, which the animal attaches at 

 pleasure by a byssus ; others are fixed to marine substances by 



the lower valve. 



1. Pedum*. 



Shell inequivalve, slightly auriculated, lower valve gaping. 

 Beaks unequal, distant. Hinge without teeth ; ligament partly 

 external, inserted in an elongated, channel-shaped pit, formed 

 in the lower side of the beaks ; lower valve notched near the 

 posterior base. 



The pedum is a free, regular, inequivalve shell ; and the sin- 

 gular notch of the lower valve shews that the animal has the 

 power of attaching it by a byssus. One Species. 



Type. Pedum spondyloideum t, (Ostrea spondyloidea. Gmel.) 



Shell cuneiform oval, rather flat ; upper valve longitudinally 

 striated ; striae rough, granular. 



Indian Seas. PI. II. Fig. 86. 



2. Lima J. 



Shell longitudinal, subequivalve, auriculated, slightly gaping 

 at one side between the valves ; beaks distant, their internal 

 facet inclining outwards. Hinge without teeth. Cardinal pit 

 partly external, receiving the ligament. 



The lima has no notch on the lower valve ; the little ears at 

 the base of the shell, though small, are distinct. Linnceus ar- 

 ' A slujihcrd's cnok. ' Resembling a sjwndylus. i A file. 



