61 



not that freedom of parts observable where room is left for increase. It is, per- 

 haps, owing to this that all the joints of the hand have laterally, where they 

 adhere near each other (Pi,, n. fig. 4. and 5.) a compressed figure, as also that 

 the first joint of the tentaculum intrudes on the second joint above it. 



The PLATED INTEGUMENT (PL. 1.) covering the abdominal cavity, is in the 

 specimen alluded to, extended beyond the scapulae, connecting the sides of the 

 arm joints and the hands as far as the first finger joint together, hence de- 

 monstrating a considerable extension of the abdominal cavity. The plates are 

 neatly arranged, forming a sort of rose-like appearance, of which a minute 

 hexagon or heptagon forms the middle. A question here suggests itself, whether 

 the animal in age loses the tentacula of the arms, and those at the commence- 

 ment of the hand? It certainly can here readily dispense with an apparatus of 

 detention, its fingers having increased in size and length, and as the costa* and 

 scapulae do not grow larger in proportion, it is obvious the covered cavity be- 

 tween them can only be increased by extending the points of adhesion of the 

 integument between the arms, to which it already adheres where it covers the 

 grooved canal at their inner surface. By dispensing with the tentacula, which 

 are no longer required, their articulating surfaces on the arms, furnish favour- 

 able points for the angular insertion and adhesion of the plates of the integu- 

 ment. The increase of the size of the abdominal cavity is rendered imperious, 

 by the extension of the viscera necessary for the receiving and preparing of the 

 greater quantity of food, required by the organic wants of an animal materially 

 increased in size and full grown. I am nearly confirmed in the correctness of 

 the above opinions, by having detected in a specimen of P. Briareus the integu- 

 ments adhering to the sides of the first arm joint, which also had no longer a 

 tentaculum, an instance of which is also represented in Mr. PARKINSON'S Or- 

 ganic Remains. VOL. 11. PL. xvni. fig. 2. 



Fragments of an animal approaching to P. Subangularis, but of a smaller 

 and neater shape, occur in the oolite at Dundry, and in the forest marble. It 

 must remain for further favourable opportunities to ascertain what claim these 

 have to a specific distinction, or whether they belong to a variety of present 

 species. 



