SAGENOCRINIDAE 23 1 



the group generally. It begins with a slight linear indentation of the plates about the upper 

 primibrachs, which runs parallel to the lateral margin, becoming sharper upward and the 

 lines multiplying until there are 6 to 10 sharply bounded grooves ; these diminish again 

 distally until in the smaller branches of the ray they are reduced to two and finally to one. 

 There is nothing in these markings to indicate any such thing as a food groove as we find it 

 along the arms in the Camerata and Inadunata, although in some plates the median furrow 

 may be the largest. They seem rather to indicate that in these forms the perisome in the 

 free part of the rays beyond the secundibrachs was firmly attached to the plates by lines - of 

 growth, in this manner supporting the ambulacra which in some cases may not have been 

 calcified. The perisome can be seen in place on some plates from the upper part of the ray in 

 Synerocrinus (PI. XLII, fig. 5&), and I am unable to distinguish any ambulacra in those 

 places. 



In the two principal specimens on Plate XXIII it will be noted that while the two plates 

 following the posterior basal are fairly large, and are perfectly united to it by suture with 

 deep fossae, their distal margin, and that of the small plates interlocking with them, have 

 for the most part the same corrugated surface as already described, indicating the beginning 

 of perisome. This is plainly shown in the plates at the left in figure la, where the corruga- 

 tion is seen on the two large plates ; it exists also on the corresponding large plates in the 

 specimen of figure 2, although not visible in this figure, while the sutures at the small trian- 

 gular space at the left, where a plate has fallen out, have deep fossae. The left side of the 

 anal interradius thus had a curved, corrugated edge continuous with that of the adjoining 

 primibrach, the same as in the regular areas ; but this is not quite the case to the right where 

 the curve does not seem to connect with the margin of the brachial, but there appears to be a 

 slight curvature in the distal face of the right hand large plate, with one or two small plates 

 next to it, which may have formed the beginning of a tube. 



Considering the additional anals at that side in De Koninck and Le Hon's specimen, and 

 the long series of plates bordering the right posterior radial in F. communis (PI. XX, 

 fig. $b), it seems probable that in this form the anal plates to the right passed into a vertical 

 series of varying extent, which, either directly embedded in the perisome or after hugging 

 the right posterior ray to near the level of the tegmen, became the support of an anal tube 

 originating not on the posterior basal, as in all the Taxocrinidae, but at some point above it 

 after the intervention of other solid plates. We have such a case, with still less intervening 

 sutural structure, in the genus Synerocrinus, which is about as near the border line of the 

 Taxocrinidae as is possible to imagine. This is probably what happened at some point in the 

 posterior interradius of every Sagenocrinoid, but it did not in most cases result in sufficient 

 differentiation of solid structures to leave the evidence of it in the fossil state. The tendency 

 toward the formation of such a tube is shown perfectly in later species of Forbesiocrinus, and 

 the tendency of the tube to lean to the right is found in every group of the Taxocrinidae. 

 This dextral series of anal plates is essentially the same thing seen in Temnocrinus, only 

 extending higher up in Forbesiocrinus communis; and a comparison of the figures upon 

 Plates XVI and XX is sufficient to show the great general resemblance between the two 

 types. 



The morphological position of the earlier Forbesiocrinus, therefore, is clearly with the 

 present family by reason of the fundamental anal structure, but with a tendency toward 

 Taxocrinus in its interbrachial and higher anal structures. The later species, of which 

 F. wortheni may be taken as a typical example, present a type which marks the culmination 

 of the division of the Flexibilia having the strong anal side. This type is the last prominent 

 survivor of the Sagenocrinidae, and in its interbrachial structure might well be taken as the 

 successor of the genus Sagenocrinus. The essential difference in anal structure between the 

 two genera may be largely due to the longer posterior basal in Forbesiocrinus, which rises to 

 about the height of the radial ; so that when it is angular the first large anal plate to the 



