426 SMITHSONIAN INSTITUTION 



O. ulrichi like figures 1, 2, 3, 10 of Plate LXVI with those of similar speci- 

 mens of 0. divcrsus on Plate LXV will show the differences better than 

 detailed measurements. As to these characters there are various intermediate 

 stages, so that if the specimens were found together in the same horizon it 

 would be almost impossible to distinguish them. Maximum specimens in the 

 same condition as the type of O. diversus measure 40 mm. length of ray to the 

 fork; 30 mm. length of ramus above fork; diameter of calyx, 38 mm.; of base, 

 9 mm. The column is rather larger, with less convex nodal ossicles ; we have 

 it to a length of 15 inches (only part shown in the drawing) in the specimen 

 figured 4, Plate LXVI, at which point cirri begin to appear, indicating a prob- 

 able length of three or four inches more. 



The number of IBr is remarkably constant at 4; in 30 specimens with sub- 

 stantially all the rays visible, 16 are regular throughout, 11 vary in one ray, 

 and 3 in two; or out of 146 rays, 135 have 4 or more, and only 11 have 3. 



The affinities of this Keokuk species are far closer with the antecedent Burlington form 

 than with either of the other two Keokuk species, which occur at a slightly higher horizon. 

 It is one of the leading fossils in the prolific crinoid bed of Indian Creek, Montgomery 

 County, Indiana, where it has been collected in two colonies about a quarter of a mile apart. 

 The horizon is in the upper part of the Keokuk group! doubtless representing the geode bed, 

 but not quite so high as the Crawfordsville bed. The crinoids were imbedded in a thin 

 stratum of bluish argillaceous limestone, very homogeneous in texture, and soft enough to 

 be easily worked with tools ; they had been deposited in very quiet waters, so that the stems 

 and arms were intact and the finer structures beautifully preserved. The specimens were 

 abundant, about 75 having been recovered in good condition for study. With these favor- 

 able conditions it has been possible to make a number of preparations which have thrown a 

 flood of light upon structures previously unknown in this genus, and have furnished the 

 means of illustrating the tegmen and the relations of the anal series to it, probably for the 

 whole group, with a completeness not before dreamed of. 



Up to the time of these discoveries nothing was known of the ventral structure of 

 Onychocrimis, although from analogy with Taxocrinus its disk was supposed to be com- 

 posed of a soft skin with calcified ambulacra. This was confirmed, and in 1906 I published 

 an account of it with figures of some of the specimens (Jour. Geology, vol. 14, p. 467). The 

 limits of that paper did not admit a full exposition of the material, a selection of which has 

 now been assembled and fully illustrated upon Plates LXVI, LXVII and LXVIII. 



In addition to the type, now further cleaned since the first figure was published by 

 Miller and Gurley, there are figured on Plate LXVI a series of specimens showing the gen- 

 eral form and proportions, with 'instructive details of the rays, ramules, interbrachial and 

 anal structures, in individuals of different stages of growth from very young to mature, all 

 in vertical position with the arms erect. The external appearance of a perfect anal tube 

 with the bordering perisome in good condition on both sides, as well as full details of the 

 mode of branching in the clusters of ramules, are shown by the beautifully preserved speci- 

 men at figure 2. Figure 4 has the stem to a distance of about twelve inches more than is 

 shown in the drawing; it continues with about the same alternation of short, non-projecting 

 columnals until toward the distal end, where they become more equal, and small scattered 

 cirri begin to appear; it was probably 18 to 20 inches in total length. The growth of inter- 

 brachials is shown by the contrast between figure 8a with its single plate in the axil, and 

 figure 3 with 20 or more iBr rising on either side in a deep crescent to the height of the 



