496 FRANK SPRINGER 



the anal plates usually preserve their rounded appearance, and do 

 not seem to form part of the calyx wall, or to be suturally connected 

 with contiguous rays. Such cases as this give rise to difficulties 

 of interpretation, because these are some forms in which the anal 

 plates rise into a single vertical series connected by suture with the 

 adjacent brachials, and flush with them. These must be distinguished 

 from the cases just alluded to, where there is a rounded, armlike 

 row of plates, so closely crowded by the rays that there is neither 

 any part of the integument visible, nor any vacant space on either 

 side, but which were evidently not joined to the brachials by suture. 

 Both cases would answer the description "anals in a vertical series," 

 and yet they undoubtedly represent the two distinct plans, which here, 

 as elsewhere, run into perplexing transition forms. 



The armlike row of plates, while not tubular, but on the contrary 

 formed of thick and solid plates, is supposed to compose the dorsal 

 support of an anal tube, formed by the outward growth of the peri- 

 some caused by the extrusion of the rectum. If we sometimes in 

 descriptions call this row of plates "tube-plates," or the "anal tube," 

 it must be understood as a conventional term — used by many former 

 writers in this sense — to avoid circumlocution, and not as implying 

 that the plates themselves are hollow, or strictly form the wall of a tube. 



Now the position of this row of plates shows in a striking 

 manner the effect of that strange influence which has modified the 

 bilateral symmetry of almost every genus in this entire group. The 

 small infrabasal is almost invariably located under the right posterior 

 ray; the radianal originates under the right posterior ray; it migrates 

 from this position upward until it disappears, but always to the right 

 of the median line; if the arms have an asymmetrical distortion, 

 it is to the right, never to the left. And so this vertical series of anal 

 plates is affected by that tendency, which persists long after the 

 radianal has disappeared. The posterior basal on which it rests is 

 excavated into a sort of shallow socket, hke the articulating facet 

 of a radial, on the right shoulder of the plate, so that we will 

 usually see a small tongue or angle of that plate rising up to the 

 left of the base of the anal plate higher than to the right ; or, if the 

 socket-like excavation is not so plain as this, the upper edge of the 

 basal is distinctly sloped to the right. 



