120 
form resembling a drop of water when it commences its 
fall has given rise to its name. 
One of the minute productions of the Ancliff Lime- 
stone. Two of the figures are magnified. 
NUCULA mucronata. 
TAB. CCCCLXXVI.— jftg*. 4. 
Spec. Char. Subrhomboidal, rounded, convex, 
concentrically sulcated, anteriorly mucronated. 
Xwo-thirds as long as wide, very minute ; the anterior 
side is drawn out in the form of a flattened spine, and is 
distinguished from the other portion of the shell by 
being suddenly flatter. 
Found at Ancliff. The lower figures are enlarged. 
NUCULA angulata. 
TAB. CCCCLXX V I . — fig. 5. 
Spec. Char. Rhomboidal, concentrically striated ; 
most convex near the beaks ; front rounded. 
Both sides of this shell are angular, and the lines from 
their extremities to the beaks are nearly straight and 
equal ; it is about half as wide again as it is long ; the 
strim upon its surface are regular fine sulci, and not very 
conspicuous. 
There are several similar species found in strata cor- 
responding with the London Clay ; but all that I have 
met with differ in form and the depth of their sulci. 
An uncommon Blackdown fossil. Magnified figures 
are given below that of the natural size. 
