286 SMITHSONIAN INSTITUTION 



growth in that position, for that would require the crown to stand at an angle from the axis 

 of the stem, which would not only be highly improbable with a large calyx supported uni- 

 formly at all sides by the surrounding water, but is negatived by the fact that careful measure- 

 ment fails to show any modification such as this would produce in the shape and size of the 

 plates, or differences in dimension between the concave and convex sides. 



I am disposed to think the phenomenon is best explained by the conditions of fossiliza- 

 tion, taken in connection with the peculiar construction of the test in this and similar species. 

 In the upper part the walls are strong, built up of a great number of small but thick plates 

 perfectly fitted together like the stones of an arch ; this afforded considerable resistance to 

 outside pressure in that part. Furthermore, it is characteristic of this genus and most others 

 of the family to have the arms tightly infolded over the tegmen, which would still further 

 strengthen the calyx there. In the lower part, as already stated, the calyx wall becomes 

 extremely thin (not over one millimeter), and this along with the loose articulation of the 

 plates among themselves rendered that part very pliant, yielding readily to pressure in any 

 direction ; just at the base the plates were necessarily thicker by reason of connection with 

 the stem. Thus there were two zones of strong construction with a weaker one interposed. 



The crown with its closely infolded arms being elongate and ovoid, . on becoming 

 detached from the stem tended to lie on its side in the soft ooze of the sea bottom into which 

 it slowly sank and became imbedded. The weight of the visceral mass caused the lower side 

 to settle at the zone of least resistance and the upper side to follow it, while the upper part of 

 the crown, being of stronger construction, retained its shape. This would make the lower 

 part of the calyx wall ventricose at the under side and concave at the upper, with the apex 

 of the base pointing upward out of the line of the axis. There is a slight tendency to the same 

 condition in /. subangularis, where in some specimens one ray is more protuberant near the 

 base than the others. The calyx in that species, being much narrower, more elongate, and not 

 having the ovoid shape that this has, yields but little and the distortion is not very marked. 



While I have not given it as a character in the diagnosis, nevertheless this distortion is 

 one of the most conspicuous features of the species as it has been usually found, which has 

 been remarked by all observers, and by which it can be instantly recognized. In a lot of over 

 one hundred and fifty specimens collected in early days by Sir William van Home, and now 

 in the University of Chicago, every one shows it in a greater or less degree. Some speci- 

 mens, otherwise similar, have less distortion than the types illustrated, perhaps owing to their 

 having exceptionally thicker walls, or more probably to their being imbedded nearly in a 

 vertical position with the base up. In two such cases among my specimens the calyx is fore- 

 shortened so that the ratio of height to width is about i to 2. In other cases there is good 

 reason for thinking they belong to different species. 



This species has been the subject of considerable controversy. It was described with a 

 diagram but without other illustration by Winchell and Marcy in 1865 in an extensive memoir 

 upon the Fossils of the Niagaran limestone of Chicago, 1 with a very incorrect conception of 

 the facts, due partly to the imperfection of their specimens, and partly to their lack of familiar- 

 ity with the crinoids. They made the distinctive characters the " small size of the stem, large 

 size of the basal plates .... the presence of two instead of three radials, and the perfectly 

 straight transverse sutures," — every one of which is wrong. 



As to the number of radials, the authors said that the characters about the base are some- 

 what obscure, and they may have overlooked the real first radial ; but this fact led them into 

 an equally great error as to the basals, to which they assigned a form that is wholly imaginary 

 and impossible. That which they called the very slender stem is the cast of the axial canal, 

 probably enlarged by the resorption of the infrabasals ; but their remark that it is "turned 

 to one side in all our specimens " shows conclusively that they had before them the form so 



1 Mem. Boston Soc. Nat. Hist., Dec. 1865, p. 



