82 SMITHSONIAN INSTITUTION 



In figure 4 the radials have notably increased in size, and above them at 

 the base of the tentacles may be seen two small disconnected plates which are 

 the beginnings of the first and second primibrachs ; the radianal is enlarged to 

 a smaller degree, and it lies to the left of the radial which now begins to curve 

 around it toward the middle of the posterior basal, as in Lecanocrinus and 

 Gnorinwcrinus ; the gut has become concealed behind the radianal except at the 

 opening which is visible at the apex of that plate. The radianal is now in the 

 stage of its first appearance in Antedon before mentioned, as described by 

 Carpenter, Thomson, Mortensen and others, and this may appropriately be 

 called the "Antedon stage." 



The next stage is represented by figures 5a and $b, posterior and anterior 

 views. The radials have enlarged until they almost come into lateral contact 

 except posteriorly; the two primibrachs have thickened and become connected 

 with the radial and with each other, the second one being an axillary covering 

 the base of the tentacles, now three in number; basals and orals have become 

 relatively smaller owing to the superior growth of the radials ; and the radianal 

 is about on a level with the radial to the right of it, indenting its left side and 

 still touching the sloping shoulders of the posterior basal, comparable to its 

 position in Forbesiocrinus and Taxocrinus. In the triangular spaces between 

 the radials and orals small plates appear which are readily recognized as the 

 interradials, formed in the same manner as other calyx plates; their position 

 is such that if they should develop downward to a connection with the basals, 

 there would be produced an interradial system like that of the Rhodocrinidae, 

 and if upward, as they actually do, like that of the Taxocrinidae. The orals 

 now exhibit rather distinct pores distally which may be analogous to those seen 

 in Holopus (PI. A, fig. 8), and in the posterior oral alone of Onychocrinus and 

 other Flexibilia. 



A specimen at about the next stage with complete stem as it appears at- 

 tached to a cirrus is shown by figure 6 of Plate B. In this and succeeding 

 stages shown by figures 7, 8a, 9, 10, of Plate B, and la, b, of Plate C, the 

 radials increase in size until they greatly exceed the basals, which now form a 

 low and nearly horizontal basin ; the interradials have been pushed upward by 

 the radials meeting below them, and have increased in number from 1 to 5 

 or 6 in the regular areas and bordering the radianal as well, where they pass 

 over into the plates of the heavily plated integument which is extended upward 

 into a large conical protuberance, now definitely constituting the anal tube, 

 analogous in form and position to that of the Taxocrinidae; the gut has con- 

 tinued to extend itself upward, until its opening is now at the apex of the- 

 conical projection rising far above the orals, which by the multiplication of 

 interbrachial plates are now being more and more separated from the dorsal 

 cup and relatively reduced in size; the radials have met and form a closed ring; 



