51 
This genus presents the best place in which I can notice the re- 
markable limpet-like shell described by Da Costa, who never saw but 
four that were entire, or nearly so. He places it among the patella ; 
and says : “ These limpets are very large, and, like the Concholepas , 
resemble a single shell of a bivalve. They seem to be of two kinds, 
and are more irregular than that shell ; and, instead of being sulcated 
lengthwise, are circularly wrought, or in a transverse manner, with 
' ^ r y irregular ridges, not thickly, but rather thinly, set. The 
s ells are very thick : one sort is high or copped, the other is broad 
or flattish. Elements of Conchology , p. 142. The specimens which 
1 possess of this fossil are not sufficiently illustrative of its form. 
I have, however, given a figure of one of them, which was found at 
Pangbourn, in Berkshire, Plate V. Fig. 3. 
III. Fissurella. A buckler-formed univalve, without spire : the 
vertex perforated, with an ovate or oblong opening. 
The species which I have obtained from the Essex cliffs nearly re- 
semble the F. lahiata, Lam. 
IV. Emarginula. An obliquely conical univalve, the vertex in- 
clined, and the posterior margin slit or notched. 
I have repeatedly found a species of this genus in the Essex cliff, 
which, in its elegantly reticulated or cancellated surface, its reclined 
vertex and its size, agrees with P.fissura, as figured by Pennant, 
a .^ . ' 152 ; and by Lister, Tab. dxliii. Fig. 28, who de- 
scri es it as Patella eocigua, alba, cancellata, fissura notabili in 
margine. 
E. clypeata, 
Three species are described by Lamarck, E. costata , 
and E. radiola. 
V. Crepidula. An oval or oblong vaulted univalve, with its apex 
inclined to one end, and its cavity partially divided by a horizontal 
pi9.tG, 
fff 0 T' a, ?! 1S - An oval vaulted univalve, the apex inclined to 
me left side, with two teeth and a sinus at the base of the right edge. 
