332 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



more convex on the right side than on the left (adjoining the "anal"), though 

 after the withdrawal of the "anal" this asymetry quickly disappears. 



The general tendency of the "anal" plate to keep to the right of the posterior 

 interradial area, though very strongly marked, does not appear ever to have attracted 

 attention; but it is nevertheless a fact of the very highest importance. 



In the young of Promachocrinus, in which the five infrabasals are large and 

 equal hi size, the "anal" appears to be formed before any of the radials, occu- 

 pying a position in the rhombic area between the corners of the basals and orals. 

 Soon afterward the radial appears, just to the right of and in line with it, between 

 the basal and oral of that side and to the right of the vertical line dividing the 

 basals and the orals. The radial grows much faster than the anal, which it grad- 

 ually surrounds, so that the latter comes to lie in a deep concavity in the side of 

 the radial to the right of it and to the right of the posterior interradius, well to 

 the right of the midline of the posterior basal. Later this right-hand radial 

 extends itself beneath the "anal" and the concavity becomes straightened out 

 and disappears, the "anal" concurrently being shoved diagonally forward (toward 

 the left) and disappearing by resorption. 



Mr. Frank Springer has shown that hi the families TaxocrinidaB and Ichthyo- 

 crinidse and hi the Inadunata there is an essentially similar variation in the posi- 

 tion of the radianal, which migrates from a primitive position directly under the 

 right posterior radial to an oblique position under the lower left-hand corner of 

 that radial, finally moving upward and becoming completely eliminated. 



The position of the so-called "anal" hi the larvae of Promachocrinus, lying 

 within a concavity in the lower left-hand portion of the radial to the right of the 

 posterior interradius, and its migration upward and toward the left, leave no room 

 for doubt that the so-called anal of the pentacrinoid larvae is nothing more nor 

 less than the radianal of the fossil forms. 



Mr. Springer, as before stated, has shown that ha the Flexibilia there is a very 

 pronounced tendency manifested by all the radial structures to turn toward the right; 

 the radianal originates under the right posterior radial; from this position it migrates 

 upward until it disappears, always to the right of the median line; if the arms 

 have an assymmetrical distortion it is toward the right, never toward the left; the 

 vertical series of plates arising from the anal x is affected by this tendency, which 

 persists long after the radianal has disappeared. 



In the ontogeny of the comatulids the radianal follows the same course as 

 in a succession of fossil genera; the anal tube is always to the right of the median 

 line of the posterior hiterradius; that the supplementary arm arising on anal x 

 hi the young of Thaumatocrinus renovatus and of Promachocrinus kerguelensis 

 does not turn to the right is to be interpreted purely as a secondary condition, 

 the result of its origin on the edge of the disk and its free extension outward from 

 the body. Were the series of ossicles following anal x in the young of Thauma- 

 tocrinus and Promachocrinus incorporated hi the perisome we can not doubt but 

 that it would have followed the anal tube hi its migration to the right, and would 

 therefore have come into complete correspondence with the conditions seen in the 

 fossil Flexibilia. 



