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larity, how difficult it is to describe them in words. In general, how- 
ever, the markings are made by lines passing perpendicularly from each 
edge of the plate, and terminating in radiating lines extending from the 
centre of the plate to each of its angles. These markings not only 
differ very considerably in different specimens, thereby forming numerous 
varieties ; but, as will be presently seen; they vary in the different series 
of the plates in the same specimen, being adapted, in some measure, 
to the different forms of the plates ; which also vary in their respective 
series, by which their better adaptation to each other is secured, and the 
required form of the animal is obtained. Their connection with each 
other is also secured, by their rays or markings so terminating at the 
edges of each plate, as to form crenulated margins, which are reciprocally 
received into each other. 
In the specimen of this animal, Plate XIII. Fig. 24, from a chalk-pit, 
in Kent, its inferior part has evidently been formed of five pentagonal 
plates, circularly disposed, two of which are seen in this view of the 
fossil, with a semicircular notch m the middle of each inferior margin. 
The surfaces of these plates have but few markings ; four or five risings 
only passing from the centre of each plate, and meeting at each articula- 
tion with similar risings in the adjoining plates. 
In the five angular recesses which result from the junction of these 
bodies, at the upper part are placed the corresponding projecting an- 
gles of the next series of five hexagonal plates ; and in five superior 
angular recesses, formed by these, are placed the corresponding pro- 
jecting angles of the third series, which are all pentagonal : each of 
these having its superior side articulated with one of the sides of a 
pentagonal plate at the top, which completes the marsupial form be- 
longing to this animal.* 
* This description is adapted to the annexed figure, which is, by mistake, placed in a re- 
versed position to that which was, perhaps, most common to the animal ; the close part of 
the purse at the bottom, and the open part from which the tentacula proceeded, at the su- 
perior part, as in the description by Mr. Donovan. 
