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the articular ridges, which at each end traverse its axis, cross each 
other, passing in opposite directions ; as is also the case with the tro- 
chites. Fig. 41. 
With the hope of learning more of the animal to which this part 
belonged, I sought for some body which, with a similar articulation, 
possessed some variation of form, and at length discovered the body, 
Plate XIII. Fig. 34, which is also attached to its matrix. These bo- 
dies are found in the same chalk-pits as yield the bodies just de- 
scribed. At the one end of this body exists a similar articulating 
surface with that of the former body; but at the other end, such a 
conformation is observable, as seems plainly to mark it as the base of 
the pelvis, from which the arms of the animal had proceeded. Five 
pentagonal pieces are first disposed in a circle on the end of the tro- 
chite, and on these are placed five other pieces,, which are rather longer 
than the former. An inferior angle of each of these is let into an an- 
gular recess, formed at the junction of each two of the former bodies ; 
and at their superior part, each of these bodies terminate in a concave 
surface, with two denticulae on its interior margin, forming, at their 
union, a surface, which bears very much the appearance of a flower 
with five petals. From this surface must have proceeded the arms, 
fingers, &c. of this animal ; to discover the structure of which was the 
next object of my research. 
Following the clue yielded by the particular species of the articula- 
tion, I am led to place next before you, as parts, in all probability, 
composing the articulated arms and fingers, the series of ossiculse, 
Plate XIII. Fig. 70, which are here depicted rather beyond their na- 
tural size. These, from the resemblance which their articulating 
surfaces bear, appear to be deserving of being classed with the 
preceding body. The middle part of these ossiculie is cylindrical, 
but the ends are contracted, as if compressed, in two contrary direc- 
tions, so that two narrow elongated surfaces are formed at each end, 
exactly crossing each other, and having a ridge running the length of 
