ICHTHYOCRINIDAE 279 



with perfectly smooth, straight, slightly alternating columnals of uniform diameter until 

 toward the distal end where it is somewhat enlarged. I have three specimens (obtained too 

 late for figuring) in which the column is preserved to a distance of about 23 cm., where a 

 branching root begins to appear. 



In average size, and the low, sharp imbrication of the plates, this species resembles 

 /. corbis; but its radial ridges are stronger, basals larger, and it lacks the low, broad, convex 

 figure of that species. Of all other species it most resembles /. pyriformis, with which Hall 

 identified it ; but the absence of surface ornament and the stronger imbrication of the plates 

 in this will readily differentiate the two. 



Angelin identified a Gotland form as /. laevis (Icon. Crin. Suec, pi. 9, fig. 17), which is 

 clearly distinct by reason of its ornamental surface, smaller basals and other characters, as 

 has been more fully shown under I. pyriformis to which it belongs, and in the discussion of 

 /. gotlandicus. 



In the year following Conrad's publication of his species and genus, Hall in the Geology 

 of the Fourth District of New York, p. ill, figure 3, published a figure of a flattened specimen 

 with part of the stem attached, which he described on page 112 under the name of Cyatho- 

 crinites pyriformis (Ichtliyocrinus laevis), declaring that he had " no doubt of the identity of 

 the fossils figured by Mr. Murchison and Mr. Conrad." Nine years later, in the Palaeon- 

 tology of New York, vol. 2, p. 195, he redescribed the genus and species at considerable 

 length under Conrad's name, stating at the same time that " the genus is known only in a 

 single species," and adhering to his former opinion, stated that " this is probably the same 

 species figured by Murchison as Cyathocrinus pyriformis, and is perhaps identical with 

 figure 2 of Miller's Cyathocrinus tuberculatum." He added : " The structure, however, shows 

 conclusively that it should constitute a distinct genus. The remarkable character of an 

 undeveloped tripetaloid base assimilates it with the crinoids having this structure, or three 

 pelvic plates succeeded by five in the second series." He gave the structure of the calyx 

 from the five pelvic plates up, and laid stress upon the tapering base and slender round 

 column as distinguishing characters ; but he did not mention the imbrication of the plates, 

 which was beautifully shown in some of his own specimens. He did, however, well describe 

 the structure by which the plates of abutting rays alternate with each other and produce the 

 interlocking so characteristic of the genus. 



Hall illustrated the species very thoroughly with figures of three specimens, accom- 

 panied by elaborate diagrams of structural details. Among them are enlarged views showing 

 the three "undeveloped" plates (infrabasals) and five "pelvic plates" (basals) (op. cit., 

 pi. 43, figs. 2a-p). I have given new figures of two of Hall's specimens, 2b and 2c, carefully 

 drawn from the original specimens (PI. XXXIII, figs. 2, 5a). By comparing my figure 2 

 with Hall's figure 2b, it will be seen that the stem is not so slender as his figure shows ; and if 

 we further compare the figures of my three specimens with stems attached to a greater 

 length than his, it will be evident that the stem, on whose thinness Hall and others following 

 him have laid particular stress, is by no means so thin as his and Conrad's figures would 

 indicate. And I have no doubt that in these and Hall's figure 2a, also showing a very thin 

 stem, the column was not freed from the matrix to its full diameter. The form of the stem 

 in this species is simply that characteristic of the genus, and is of the type which extends 

 through almost the entire group ; that is, large at the junction with the base and composed of 

 very thin columnals, tapering gradually for a short distance and then becoming cylindrical, 

 with alternating short and long columnals. 



Billings 1 in 1856 published a description of this species, which was taken from Hall, 

 and gave no additional information. Hall's figure 2a, evidently made from the same speci- 

 men as his first figure in the Geology of the Fourth District, 1843, p. Ill, figure 3, has been 

 copied by S. A. Miller ; his figure 2b by Von Zittel and others. Pictet's plate 100, figure 17a 



1 Canadian Naturalist and Geologist, vol. 1, p. 59. 



