141 
expected between it and the cup-like portion of the Crinoidea inarticulata, the 
Comatula, Marsupites, and Euryale, became apparent, 
The five plates at the bottom of the cup thus presented, pierced for the 
passage of the oviducts, appeared to represent the pelvis, on which 
forming the area and areole are arranged in series analogous to costals and 
intercostals of the former, and from these (the scapul and arms being deficient 
in this order) a plated integument extends across the abdominal cavity inclos- 
ing in the centre the mouth ; this, however, is armed with five teeth, inserted 
in a complicated ossicular apparatus, a character which, as far as my know- 
ledge extends, does not appear to have been possessed by any of the Crinoidea, 
the plates 
It is evident that the original texture of the ossicular plates of the Crinoidea, 
Stelleride, and Echini, must have been similar, since the same peculiar struc- 
ture of calcareous spar is exhibited in the fossil remains of all these substances. 
As the muscular integument over the plates does not extend over the whole 
shell in an uninterrupted line as in the Crinoidea, where it is intended to effect 
the movement of the arms, but is limited to short spaces from tubercle to tu- 
bercle, each muscle having for its office the erection of a single spine, a similar 
conspicuous appearance cannot be expected. 
In recent specimens of Cidaris imperialis, we notice slight radiating 
ridges on the areas surrounding the mamillz, evidently the result of the depres- 
sion of the calcareous matter during secretion, in consequence of the frequently 
repeated contracting action of the fibres of the radiating muscle. 
In fossil specimens of a similar Cidaris occurring in the coral rag, 0 
figured in ParxissoN's Organic Remains, Vol. 111. Pr. 1. fig. 9. we trace some- 
times immediately below the mamilla a radiating marking. . Is this not the 
muscle in a petrified state ? 
The corrugation of the muscular membrane investing the regions round the 
vent, and the undeveloped spines near it, is, I apprehend, the cause of the sin- 
gular appearance exhibited by some fossil specimens of a Cidarites from Wilt- 
shire,asrepresented by Mr. Parkınson, in his Org Remains, Vol. ru. Pr. 1. fig.13. 
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