SAGENOCRINIDAE 221 



Sagenocrinus americanus Springer 

 Plate XIX, fig. 5 



Sagenocrinus americanus Springer, American Geologist, XXX, 1902, p. 88, text-fig. 



A relatively small species. Crown elongate, with short arms. Calyx tur- 

 binate, side outline straight; height to width at IIBr 3 , 1.2 to 1 ; spread of calyx, 

 1 to 3. Plates smooth, without ridges ; radial and brachial series with decided 

 sinuous sutures. Crown, 29 mm. high by 19 mm. wide; base, 6 mm. 



IBB in erect pentagons relatively higher than in >S\ expansus. BB the 

 largest plates in the calyx. RA obliquely below r. post. R, partly between BB, 

 but not touching IBB. Anal x larger than iBn, or the succeeding plates in anal 

 area. iBr in not over 5 ranges ; illBr few. RR much smaller than BB. IBr 2 ; 

 I IBr 3. Arms slender and apparently short. Column large, tapering but 

 slightly from the calyx, with slight alternation of thin and thicker columnals. 



As but one specimen of the species is known, it has been thought possible that some of 

 the characters above given may be individual, especially the position of the radianal, which 

 departs from the typical form of the genus in not being within the basal ring and therefore 

 not passing down to the infrabasals. It is more probably, however, a specific character cor- 

 relating with the greatly increased size of the basals, which tended to crowd it upward to 

 make room for themselves. The difference in relative size of the calyx plates between this 

 and the other species is very marked, the radials being the largest plates in 5". expansus, while 

 here the basals are much the largest ; this produces a higher and much less expanding calyx, 

 as a comparison of the measured proportions will show. The arms are of extreme delicacy 

 for this genus, and must have been short, as they infold and disappear from view between 

 the first and second bifurcations after becoming free. These features, together with its well- 

 marked sinuous sutures extending from radials into the arms, impart to this form a very 

 different aspect from that of any specimen of the other species. 



The position of the radianal inclined me at first to doubt if this species could be held 

 within the genus ; but further consideration showed that the difference is rather one of 

 degree than of kind, and relates to a character which is somewhat variable in the typical 

 species. The radianal of typical Sagenocrinus is not in the position of an infer-radial directly 

 at the base of the ray and connecting" with the radial of the adjacent ray, as is the case with 

 all forms having the radianal in the primitive position ; it has shifted from that position, and 

 although resting very low down, within the ring of basals, it lies nevertheless obliquely out- 

 side of the ray, and belongs to the anal, or interradial, rather than to the radial structures. 

 Variability in the extent to which it has grown either upward or downward may therefore 

 well exist within the same genus. 



The type specimen is from the Waldron beds of the Niagaran at the noted fossil locality 

 at Conn's Creek, near Waldron, Indiana, and was obtained by the author many years ago from 

 Dr C C. Washburn, the veteran collector resident at the locality, whose extensive collection 

 afterward passed to the University of Chicago. It is singular that among the many collections 

 made in the same beds during more than 40 years no trace of another specimen was ever 

 found. The horizon is considerably below that of 5. clarki, and this may account for the great 

 difference of this species from that, in all the characters wherein the latter resembles the 

 European form. 



Type. Author's collection. 



Horizon and locality. As above stated. 



