BASAL PLATES IN CRINOIDEA CAMERATA 543 



The simple basal is in general symmetrically enlarged, and the 

 base is occasionally a regular pentagon. 



In the Stephanocrinidae and Pentremitidae the reduction of 

 the compound basals is bilaterally symmetrical, and is usually 

 accompanied by reduction of the radials directly supported by the 

 compound plates. This reduction is compensated for on the anterior 

 side by lateral growth of the simple basals and the radials obliquely 

 supported by it. On the posterior side, however, distortion has 

 taken place. If absorption had caused the reduction, either plate 

 shoving or shrinkage of the sarcode would be necessary to keep 

 the plates in contact; but plate shoving is apparently impossible, 

 and shrinkage of the sarcode improbable. Upon comparison of 

 the ornamentation in the reduced and unreduced radials in Ste- 

 phanocrinus , another change seems to have taken place. The 

 neural ridges of the reduced radials are fused, farming a single 

 broad ridge, which apparently indicates that the underlying nerves 

 are in closer relation than in the other radials. The reduction 

 seems, then, to have been caused by the inhibition of lateral expan- 

 sion in the sarcode in the reduced areas, and not to absorption, and 

 is a very good example of deep-seated atrophy. In the three- 

 basaled, hexagonal Camerata, anchylosis and reduction of the basals 

 are complicated by the appearance of the anal plate, and cannot 

 now be considered. 



2. DELAYED ANCHYLOSIS 



In many genera, especially of the hexagonal Camerata, anchy- 

 losis takes place at such an early period in development that no 

 trace of the immature forms with unanchylosed basals is preserved. 

 The only hope, then, of locating the missing suture is by delayed 

 anchylosis, or characteristics of ornamentation. Ornamentation 

 has, however, received so little study, and the subject is so broad, 

 that the writer cannot at present give it adequate consideration. 

 Examples of delayed anchylosis, however, are not unknown, and a 

 number of cases will be cited in the latter part of this paper. 

 Delayed anchylosis is simply a nascent stage of anchylosis, due 

 to the inhibition of activity in the ameboid calciferous cells. It 

 may appear in the form of internal or external grooves, or in its 



