MAMMALIA OF THE PURBECK BEDS. 
325 
Fig. 302. 
Cyprides from the Middle Pnrbecks. 
a. Cypris striato-punctata^^.Yoxhe^. h. Cyprisfasciculata,lEi»'¥oY\)QS. 
c. Cypris granulata, Sow. 
this bed Professor Forbes discovered the first echinoderni 
(Fig. 301) as yet known in the Purbeck series, a species of 
JlemicidariSj a genus characteristic of the Oolitic period, and 
scarcely, if at all, distinguishable from a previously known 
Oolitic fossil. It was accompanied by a species of Perna. 
Below the Cinder-bed fresh-water strata are again seen, filled 
in many places with species of Cypris (Fig. 302, a, ^, 0 ), and 
with Valvata, Paludina^ Planorhis^ Lim- 
nma^ Physa (Fig. 303), and Cyclas^ all 
different from any occurring higher in 
the series. It will be seen that Cypris 
fasciculdta (Fig. 302, b) has tubercles at 
the end only of each valve, a character 
by which it can be immediately recog¬ 
nized. In fact, these minute crustaceans, Foihes. 
almost as frequent in some of the shales ^ e m ec . 
as plates of mica in a micaceous sandstone, enable geologists 
at once to identify the Middle Purbeck in places far from the 
Dorsetshire cliffs, as, for example, in the Vale of Wardour in 
Wiltshire. Thick beds of chert occur in the Middle Purbeck 
filled with mollusca and cyprides of the genera already enu¬ 
merated, in a beautiful state of preservation, often converted 
into chalcedony. Among these Professor Forbes met with 
gyrogonites (the spore-vessels of Chard)^ plants never until 
1851 discovered in rocks older than the Eocene. About 
twenty feet below the “ Cinder-bed ” is a stratum two or 
three inches thick, in wMch fossil mammalia presently to be 
mentioned occur, and beneath this a thin band of greenish 
shales, with marine shells and impressions of leaves like those 
of a large Zostera^ forming the base of the Middle Purbeck. 
Fossil Mammalia of the Middle Purbech —In 1852,* after 
alluding to the discovery of numerous insects and air-breath¬ 
ing mollusca in the Purbeck strata, I remarked that, although 
no mammalia had then been found, it was too soon to infer 
* Elements of Geology, 4th edition. 
Fig. 803. 
