)
(FIGURE 159. Cyrena semistriata. Hempstead Beds.)
1. The uppermost or Corbula beds, consisting of marine sands and clays, contain
Voluta Rathieri, a characteristic Lower Miocene shell; Corbula pisum (Figure
158), a species common to the Upper Eocene clay of Barton; Cyrena semistriata
(Figure 159), several Cerithia, and other shells peculiar to this series.
(FIGURE 160. Cerithium plicatum, Lam., Hempstead.)
(FIGURE 161. Cerithium elegans. Hempstead.)
(FIGURE 162. Rissoa Chastelii, Nyst, sp. Hempstead, Isle of Wight.)
(FIGURE 163. Paludina lenta. Hempstead Bed.)
2. Next below are fresh-water and estuary marls and carbonaceous clays in the
brackish-water portion of which are found abundantly Cerithium plicatum, Lam.
(Figure 160), Cerithium elegans (Figure 161), and Cerithium tricinctum; also
Rissoa Chastelii (Figure 162), a very common Kleyn Spawen shell, and which
occurs in each of the four subdivisions of the Hempstead series down to its
base, where it passes into the Bembridge beds. In the fresh-water portion of the
same beds Paludina lenta (Figure 163) occurs; a shell identified by some
conchologists with a species now living, Paludina unicolor; also several species
of Lymneus, Planorbis, and Unio.
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