206 Dr. F. A. Bather on the Homologies 



course is followed by the Eupachycrinus series. In many 

 allied forms (e. g., Delocrinus) it is plain that the radianai 

 Lad disappeared before the migration of the other anals from 

 the cup was complete. There is no evidence that the radi- 

 anai ever followed those plates outside the cup limits. It 

 could only do so by losing its primitive morphological con- 

 nection with the lower end of r.post.R., a connection which it 

 invariably retains throughout the manifold modifications of 

 the anal area. The fate of the radianai, as indicated by the 

 fossils from Cambrian to Permian, is to disappear by atrophy 

 or resorption while still below the upper margin of the dorsal 

 cup. In the fossils from the Trias to the Pleistocene no 

 trace of it is found. 



In the Monocyclic Inadunata the history of the radianai 

 is somewhat different. In the Pisocrinidae and their descen- 

 dants it is pushed to the right of r.post.R. instead of to the 

 left, and is eventually squeezed out of existence at the lower 

 end of the cup ; it never rises between the radials. 



In the Palaeozoic Flexibilia Impinnata the radianai may 

 assume a position abutting on anal x, similar to that in 

 Botryocrinus (vide supra) } or it may remain below r.post.R., 

 or even be thrust down into the basal circlet. The essential 

 point in the present connection is that no part of it ever rises 

 between the radials, as in the Dicyclic Inadunata. The facts 

 are given by Springer (1906, Journ. Geo!, xiv. pp. 516-519). 

 If any Of the later crinoids, including the comatulids, are 

 descended from the older Flexibilia, and correctly classed as 

 Flexibilia Pinnata, then it is important to note that the radi- 

 anai has not been observed in the adult of any one of them 

 from Triassic to Recent times. 



Returning to anal x, and confining our attention to the 

 Dicyclic Inadunata, we find it beginning in Ordovician 

 genera above, or partly above, or between the two posterior 

 radials. In the last two cases it rests on the posterior basal, 

 but if a radianai be present it abuts or in part rests also on 

 that plate. It sinks furthest down into the cup in forms 

 with a wide anal area, such as Carabocrinus and Thenaro- 

 criaus, or in the peculiar Gasterocomidae, where the anus 

 opens on the side of the cup itself. Further width is attained, 

 especially in Poteriocrinus and its allies, by the sinking of 

 right and left tube-plates (rt and It) into the cup, the former 

 even meeting the radianai. The extreme of this development 

 is reached in some Lower Carboniferous genera, such as 

 Woodocrinus. Then begins the consolidation of the cup and 

 the raising of the viscera. As the rectum passes upwards, so 



