NEW RESEARCHES 8 1 



rhombic spaces between the corners of basals and orals; but in one of these 

 spaces the radial is wanting, and in its place there is a somewhat larger plate 

 similar in composition to the others, which is attached % to the anal end of the 

 intestine, now plainly visible at the outer surface of the calyx. This plate is 

 the radianal, which now lies in the position which the radials occupy in the 

 other areas, being at the foot of the area to be occupied by the right posterior 

 ray. This position, therefore, is essentially that which is held by the radianal 

 in the earliest genera of the Flexibilia, Protaxocrinus, Ichthyocrinus, etc., 

 called the primitive position ; and it is also the position indicated for the primi- 

 tive radianal in my hypothetical figure of 1906 before mentioned (PI. A, 

 fig. 7). The anus is also in the position which it permanently occupied in some 

 Paleozoic genera of the Inadunata, viz., the zone of the basi-radial sutures. 

 In this first specimen the calcareous reticulation is so thin and translucent that 

 by transmitted light the complete alimentary system is plainly visible, consist- 

 ing of the oesophagus, stomach, and dextrally coiled intestine, as shown in the 

 figure, which will be more fully described presently ; the closure of the orals has 

 compressed the mouth of the oesophagus so that its margin appears crenate or 

 folded. 



There are two specimens in which this stage is distinctly shown, and it 

 may for convenience be called the " Actinomeira stage." The second specimen 

 is shown in Plate B, figure 2a; in this the orals, while of the same relative size, 

 are slightly parted and the oral tentacles project between their summits but 

 have not yet branched; as in the first specimen the radial of the right posterior 

 ray has not appeared, but its place is occupied by the radianal attached to the 

 gut. Although the projecting tentacles make this specimen appear the more 

 advanced, the radianal is smaller than in the other one; the difference is due to 

 the slight opening of the orals, which stretches the mouth so that its upper 

 edge is without wrinkles (fig. 2b). 



In the next stage represented (PI. B, fig. 3) the right posterior radial has 

 appeared, and beneath it to the left is the rapidly enlarging radianal attached 

 to the gut, which is still visible through the thin reticulate stereom of the 

 calyx wall just below the anal opening. The disparity in size between the two 

 plates is important as tending to confirm the antecedent appearance of the 

 radianal in the first stage, and its status as an independent element. The aper- 

 ture of the gut is here very distinct, and the intimate attachment of the plate 

 to the gut just below the opening is evident. 



1 While there is probably no direct attachment of the radianal to the hind gut, except that it lies close 

 to the anus in the sarcode that is attached to the gut, the word " attached " is used here and throughout 

 this discussion to express the intimate degree of association between the radianal and the hind gut, which 

 in behavior is more that of attachment than of association. 



