58 CONTRIBUTIONS 
so deeply impressed immediately before the beak, as to 
give a curve to the margin resembling a fracture. The 
impressa resembles very closely the figure of L. mitis 
(Sowerby). He says in his description, “no lateral teeth.” 
This species has them most distinctly marked. He de- 
scribes the margin as crenulate—ours is beautifully so. 
L. papyracea. Plate 1. Fig. 31. 
Description. Shell orbicular, lenticular, somewhat in- 
flated, concentrically and finely striated, slightly folded 
behind and subemarginate ; substance of the shell thin ; 
lunule cordate ; beaks rather pointed ; lateral teeth scarce- 
ly perceptible ; anterior cicatrix short ; lines of growth 
indistinctly marked ; cavity of the shell rather shailow ; 
margin crenulate. 
Diam. 3-20ths, Length 7-20ths, Breadth 7-20ths, of an inch. 
Observations. This species has a general resemblance 
to the impressa, but differs in being rather less inflated and 
in being without the deep impression before the beaks. 
The posterior fold of the impressa is greater, and the lateral 
teeth are much larger. In the present species the striee de- 
crease in number on the posterior part and there become 
squamose. 
L. lunata. Plate 1. Fig. 32. 
Description. Shell anteriorly oblique, inequilateral, in- 
fated, concentrically striated and furrowed ; substance of 
the shell thick; lunule broadly cordate ; beaks elevated, 
