28 SMITHSONIAN INSTITUTION 



the crown (PI. VII, fig. ib); these were probably littoral or circumlittoral 

 species living in shallow water where they were exposed to currents. The 

 longest stem occurs in Onychocrinus, attaining in O. ramulosus a length of 

 36 inches, ending in a point with lateral root branches. This was probably the 

 prevailing mode of attachment to the sea bottom; but there are a few cases 

 in which the stem ends in a flat or encrusting plate for attachment to other 

 objects, as in Calpiocrinus above cited, and in at least one species of Taxocrinus 

 (PI. L, fig. 1); these are sporadic appearances of a character which becomes 

 general in the Mesozoic Apiocrinidae. 



Cirri are rarely observed, and were probably absent in most of the genera, 

 as in the Apiocrinidae ; when present, they are usually in the form of radicular 

 branches toward the distal end (PI. LXXI). Regular lateral cirri, extending 

 for the full length of the stem, as in some Camerata and Inadunata and in 

 many Recent stalked crinoids, are unknown, and probably did not exist in this 

 group. In the few instances where cirri have been observed along the stem for 

 some distance from the bottom, they are rather far apart, and their distribution 

 irregular; they usually occur in broken whorls, one or more of the potential 

 five being missing. Those which are present maintain their proper relation to 

 the primary nerve cords, thus falling into five interrupted longitudinal rows. 

 They are given off horizontally, and the sockets are confined to the nodal 

 columnals as in Isocrinus asteria and /. zuyville-thonisoni. The radicular cirri, 

 which are usually much larger, are also given off from single ossicles, but 

 stand at an oblique angle with the stem, resting in deep, funnel-shaped sockets, 

 which involve three or four other ossicles (PI. LXXV, figs. 15a, b). 



The axial canal and lumen of the stem will be considered under the next 

 head. 



Distalwards the columnals undergo a variety of modifications in different 

 genera. In some they remain smooth and even, without alternation (Nipte.ro- 

 crinns) ; in some they alternate irregularly between long and short (Lecano- 

 crinus), and in others rather regularly (Calpiocrinus) ; in some they change 

 from alternating to uniform (Pycnosaccus) ; and in some they are strongly 

 convex like a string of beads (Hormocrinus) ; in one rare species there is an 

 almost uniform taper from the calyx to the distal end, with very short and 

 decreasingly wide ossicles in the upper half and changing in proportion from 

 six times wider than long proximally to four times longer than wide distally 

 (PI. XIII, fig. 11a) ; again the stem may enlarge in the median part and then 

 taper off toward the distal end (PI. LII, fig. 4). As in the Recent crinoids, 

 the stem ossicles are proportionally much the longest in young specimens 

 (PL LVI, fig. 10). 



The differences noted are not always constant for the genus. Complete 

 stems are rather rarely found, so we do not know as much about them as is 



