141 



expected between it and the cup-like portion of the Criuoidea inarliculata, 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 the plates 

 forming the area and areolte are arranged in series analogous to costals and 

 intercostals of the former, and from these (the scapulae 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. 



It is evident (hat the original texture of the ossicular plates of the Crinoidea, 

 Stelleridsr, and Echini, must have been similar, since the same peculiar struo 

 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 mamillaB, 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, and 

 figured in PARKINSON'S Organic Remains, Vol. in. PL. i. 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. PAUKiNSON.inhisOrg Remains,Vol.in.PL i.fig.13. 



