62 F. A. HATHKR, CRIN01DEA OF GOTLAND. 



adjacent plates the same relation as did the two plates in Castocrinus; that is to say, the 

 stem of the T lies between the infer-radials, and touches the posterior and right anteriör 

 basals, while the branehes of the T abut on the Ikfge radials. This is substantiallv the 

 same reading of the T-piece as I gave in April, 1890 (op. cit., Pl: xiv, tig. 10), with the 

 exeeption that what were then called costals are here called super-radials. Examination 

 of specimens, however, enables me to put this view forward with far more eontidence 

 than when I had to overcome the dittieulties presented by Dr. Ringuebergs drawings. 

 The opinion of Dr. RiNGUEBERG, tliat the »lateral arms and central bodys of the T-piece 

 »probably represent the tirst atial plate, while the interiör process is representative of the 

 azygous plate which has been anchvlosed to it», involves the disappearance of the right 

 ]>osterior and right anteriör super-radials, and has no counterbalancing advantage. 



In (\ilceocrinus the two halves of the left anteriör radial are roughly triangulär in 

 shape. In some of the European speeies they still touch by their apices, though not 

 necessarily in all specimens of the speeies; in the American speeies, however, according 

 to Ringueberg, they are always separated by the large radials. The anteriör and left 

 posterior radials are still wider than in the previous genera, and curve right round to 

 the stemward side of the drooping cup. The radianal and the corresponding right anteriör 

 infer-radial are distinct in most European specimens: according to Ringueberg they are 

 fused with the large radials, but I much doubt whether this is the case in all American 

 speeies, though it appears to be so in some. Between these two plates lies the T-piece, 

 now, however, reduced in size, often merely a wide quadrangular plate, and no longer 

 touching the large radials with its cross-branches. Atrophied though it be, it is still the 

 homologue of the coalesced right posterior and right anteriör super-radials. In some spe- 

 eies this plate is so minute as to be with difficulty visible. The anal x is supported by 

 the T-piece, but usually rests also by its corners on the radianal and right anteriör infer- 

 radial; it is now a wide, low and somewhat curved plate. 



In the further evolution of the family through Devonian and Carboniferous times, 

 it appears that the radianal and right anteriör infer-radial, supposing that they did not 

 become fused with the large radials, became still more diminished in size. Examination 

 of specimens of C. ventricosus (or its varieties), in the British Museum and the Riks- 

 museum at Stockholm (Plate IV, tig. 137), leads me to suppose that, in this speeies at least, 

 the T-piece has disappeared, while the right posterior and right anteriör infer-radials meet 

 one another and support together the anal x, which plate also rests by its lower truncated 

 corners on the corners of the large radials. This explains the description of the posterior 

 side given by Wachsmuth and Springer (Rev. III: 280, Proc. 1 S<S<5, p. 204): »Anal plates 

 two, resting against the basals and the incurved wings of the lateral radials. Their upper 

 side supj)orts a row of very large and heavy quadrangular ]>lates.» The only difference 

 is that what they eall »anal plates» I call »infer-radials». The discrepancy between the 

 description given by these authors and that given by Ringueberg, is due to their having 

 studied Carboniferous speeies while the latter based bis on Silurian speeies: both are right. 



We see then that in the evolution of the Galceocrinidse, the anal area j)asses through 

 four fairly distinct stages (text-tig. 13 a, b, c, d). These changes are accompanied by others 

 in the arms, the basals and so forth, all connected with the typical feature of the family, 



