524 AVICULIDiK. 



Species of Vulsella. 



liians, Lam. ovata, Lam. 



lingulata, Linn. rugosa, Lam. 



minor, Chem. spongiarum, Lam. 

 mytilina, Lam. 



Fam. AVICULID^E. 



Mantle freely open, margins cirrliated; no siphons. 

 Palps large. Foot small, cylindrie, furnished with a byssal 

 groove. Adductor muscles very unequal, one being much 

 larger than the rest. 



Shell sub-inequivalve, foliated, pearly within, composed 

 of prismatic cellular substance, and the interior of true 

 nacre. Ligament marginal, sub-linear, either interrupted 

 by indentations or serial teeth, or wholly simple. 



Genus AVICULA, Klein. 



Shell oblique, inequivalve, fragile, rather smooth ; right 

 valve most convex ; a sinus in the left for the passage of 

 the byssus. Hinge-line straight, the extremities produced, 

 the anterior caudiform or beaked ; a single cardinal tooth 

 in each valve under the beaks. Ligament partially external, 

 linear. Pallial impression entire ; muscular scars two or 

 more, one very large, the others small. 



Syn. Pteria, Scopoli. Anonica, Oken. Glaucus, Poli. 



Ex. A. hirundo, Linnaeus, pi. 122, fig. 5. Shell, A. 

 hirundo, fig. 5, a, 5, b. 



