MOEPHOLOGICAL PAET. 39 



about three feet, — one, not quite complete, being that of a large Megistocrinus 

 Evansi, the other, which is perfect, of a Strotocrinus regalis, two of the largest 

 known species. That seems to have been about the maximum length, and 

 it may be safely asserted that the stem in the majority of the older Crinoids 

 was not much over a foot long. Some stems are proportionally wider at the 

 top, and taper all the way to the root; others are larger at the distal end 

 than at the proximal ; while still others are widest in the middle. 



The root is even more variable. Its form was evidently accommodated 

 to the conditions of the place of its attachment. When attached to a solid 

 substance, it was flattened at the distal face, the radicular cirri spreading 

 out horizontally ; but when growing on an oozy bottom, it gave off long 

 vertical and lateral branches, entering the mud. 



The stem is either circular, elliptic, pentangular, stellate, semilunate, or 

 quadrangular, changing from angular to round on approaching the root. It is 

 composed of joints, which vary often considerably in size. Certain of these 

 joints, which have been denominated " nodal " joints, are separated from each 

 other by intervals of different lengths, which are filled by internodal growth. 

 The nodal joints are not only longer than the internodal ones, but also 

 wider, and, as a rule, increase in length downward. Their diameter is 

 greatest in the upper part of the stem, where in some species of the Came- 

 rata it is often twice, and exceptionally three times, that of the internodal 

 joints. The projecting margins are sometimes knife-like, the edges occa- 

 sionally crenulated, spinous, or nodose. The greater amount of length 

 which characterizes these joints, however, does not extend to their full 

 thickness, but is more or less restricted to the projecting margins, the 

 middle part at both ends being depressed, so as to enclose wholly or in 

 part the adjacent internodals. 



In the growing Crinoid, the stem constantly increased in length by the 

 production of new joints, introduced either directly beneath the calyx, or at 

 some distance from it. The joints which are formed at the proximal end of 

 the stem gradually developed into nodal joints, and all those intervening 

 comprise the internodal joints. The nodal joints of the Inadunata and 

 Camerata, and also of many of the later and recent Crinoids, were intro- 

 duced directly beneath the basals and infrabasals respectively, so that the 

 uppermost joint was always the youngest joint of the stem. But in the 

 young Comatula, in which the top joint subsequently develops into a centro- 

 dorsal, in the recent Mesozoic Millericrinus, and probably in the recent Rhizo- 



