226 



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 form- 

 ing 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 crenu- 

 lated 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 pen- 

 tagonal plates, circularly disposed, two of which are seen in this view 

 of the fossil, with a semicircular notch in 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 meet- 

 ing at each articulation 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. 



