44^ SMITHSONIAN INSTITUTION 



3. A remarkable species figured by Kirk under the name Edriocrinus dispansus, 1 also 

 from the Linden formation of western Tennessee. For years there appeared rarely among 

 Helderbergian collections from that area certain thick, broadly rounded, discoid bodies of 

 apparently crinoidal nature, having a more or less indented depression on the undifferen- 

 tiated rounded surface, while the opposite side is marked by both concentric lines of growth 

 and radiating ridges (resembling those seen in Apiocrinus; De Loriol, Crinoids de la France, 

 pi. 45, fig. 2a), — the latter dividing that surface into five large triangular spaces, and a sixth 

 about half as large. These disks proved to be the fused basals of a species of Edriocrinus 

 of a habitus widely different from any before known, and the acquisition of several good 

 specimens enables me to give a more complete description of the calyx. The radials are 

 large, in form of triangles with truncate apex; they narrow to less than half their width 

 from the proximal to the distal face, which is entirely filled by the arm facet. The anal 

 plate, narrower and narrowing upward to a lesser degree, completes the circlet, which thus 

 forms a low, truncated, obscurely hexagonal pyramid, contracting at the arm bases to less 

 than half its diameter at the base (PI. LXXVI, figs. 1, 2). The radiating ridges on the 

 ventral side of the basal disk coincide in position with the interradial and radio-anal sutures, 

 as if marking some kind of divisions at the bottom of the visceral cavity. The dorsal side 

 of the disk is usually marked by a shallow concavity or an indented scar of much less than 

 its own width, in which a small shell or other foreign object is sometimes still attached — ■ 

 showing that the base before becoming free often far outgrew its surface of attachment. 

 No trace of arms has been seen ; they must have been relatively small. The specimens range 

 from 12 to 30 mm. width at the base, the calyx to the level of the arm bases being about one- 

 half as high as wide, and its diameter at the apex about two-fifths that at the base. One of 

 the detached basal disks (PI. LXXVI, fig. 3) shows at the ventral side 4 perfectly distinct 

 basal plates, the interbasal sutures being marked by lines of infiltrating matter of different 

 color from that of the plates. The extreme contraction of the calyx at the arm bases is a 

 striking character of this species, and is at variance with the structure of the Crinoidea 

 generally. 



There is another ■ small form in the Linden formation of western Tennessee that is 

 always broadly attached by the fused base. It occurs sparingly at the same locality with 

 E. dispansus, and at localities along the Tennessee River, adhering to shells larger than 

 itself, and especially to the bulbous roots of Scyphocrimts (Camarocrinus) . Only the fused 

 bases have been seen, which are rather thin and delicate, tending to spread out upon the 

 contact surface to a width exceeding their diameter at the distal face, instead of being 

 rounded as if to become free. The specimens range from 5 to 10 mm. in diameter. Radiat- 

 ing ridges appear on the ventral surface as in E. dispansus, indicating a rather mature stage 

 of growth, and also the possibility that this form had a similar pyramidal calyx. It may be 

 the young stage of that species, or may represent a distinct species bearing the same rela- 

 tion to it as E. holopoides to E. sacculus. Adopting the latter view, it may take the name 

 Edriocrinus adhaerens (PL LXXVI, figs. 16-18). 



4. As originally stated by Hall, it has been generally assumed by authors that Edrio- 

 I'r'mus was sessile in the young stage, but became free when adult. The acquisition of a large 

 quantity of unusually fine material from the Oriskany formation in the typical locality for 

 E. sacculus at Cumberland, Maryland, enables me to throw some light on this question also. 

 The occurrence at Cumberland is the only one in which this crinoid has been found with the 

 arms complete. The prevalent form, hitherto identified only as E. saccidus, attains a much 

 larger size than those of other localities, and the fused basals of the free floating stage are 

 found by the hundreds. With few exceptions these expand toward the radials in the form 

 of an inverted cone, rounded and rather narrow at the lower extremity, the upper edge 

 more or less oblique to the vertical axis. The wall is double, enclosing a space which was 

 evidently occupied by. fibrous or porous structures; the inner surface is often marked by 



1 Proc. U. S. Nat. Mus., vol. 41, 1911, p. 112, pi. n, figs. 1, 2. 



