134 



ANNULOIDA. 



being transversely striated. Along the lateral margins of each 

 pseud-ambulacrum is a row of minute pores, which open into 

 internal sacs, and are believed to have had a respiratory func- 

 tion. Along each side of the longitudinal groove of each 

 pseud-ambulacrum there appears to have been attached a row 

 of small jointed processes or " pinnulae." The five pseud- 

 ambulacra, radiating from the summit of the calyx, give the 

 upper surface of the body somewhat the appearance of a 

 flower-bud ; hence the name applied to the order (Gr. blastos, 

 a bud ; eidos, form). Upon the whole, it would seem most 

 probable that the pseud-ambulacra of Pentremites represent 

 the arms of the Crinoids, anchylosed with the calyx, and that 

 the longitudinal furrows of the pseud-ambulacra represent the 

 " brachial grooves " of the Crinoids. 



Fig. 85. Blastoidea. A, Pentremites ftriformU, side-view. B, Base of the same. 

 C, Summit ofPeHtnmiies conoideus. b, b, Basals ; d, d, Radials : /, /, Pseud-ambulacra. 

 C Shows the central pentagonal aperture, surrounded by the five openings at the summit 

 of the deltoid plates. Carboniferous. 



At the summit of the calyx of the Blastoidea are usually six 

 apertures. One of these is larger than the others, and is 

 placed in the centre of the calyx, at the point towards which 

 the grooves of the pseud-ambulacra converge. This central 

 aperture has generally been regarded as the mouth, but Mr 



