330 SMITHSONIAN INSTITUTION 



more or less angular, interlocking or closely abutting on the outer sides, and 

 meeting above iBr, when present; axillary plates frequently marked by small 

 nodes; rami equal, tapering very gradually; ramules small, 9 or 10 in mature 

 specimen before infolding; first and second ramules usually on fourth and fifth 

 IIIBr, and above that on every third, or in the distal parts every second, brachial. 

 Column large, expanding next' to calyx for about 25 ulniformly thin ossicles, 

 beyond which longer rounded columnals begin to alternate with them, these in 

 turn doubling their length with increasing intervals between them. 



This species, rare except at one place, has always attracted much attention from the Bur- 

 lington collectors, who were careful to save every fragment found. Nearly all of these, 

 amounting to about 25 specimens from the principal collections made during fifty years, 

 are in the Museum of Comparative Zoology and in my own collection. All are derived from 

 the same horizon within a very limited area, and they have a common facies which seems to 

 mark them as one species. This includes specimens with rays and arms interlocking to 

 various heights, some with arms diverging above the axillary leaving a vacant space, and 

 others with one or two, rarely three, interbrachials ; some of the smallest specimens have 

 interbrachials, and the largest none ; and there are all kinds of intermediate stages. Also 

 while the ramules above the first two usually occur on every third brachial, an occasional 

 specimen (like PL XLIII, fig. 9) has ramules relatively so large and far apart as to approach 

 dichotomy. But the general type is definite and easily recognizable ; all have the sharply 

 pentagonal calyx, angular rays, and basals visible outside the column. The tendency to 

 develop nodes on the axillaries and lower brachials is quite constant in many specimens, but 

 it cannot be said that there is such a gradation from these to the immense spines of 

 W . spinifer as to require their consolidation into one species. 



The species was named in honor of Dr. Otto Thieme, of Burlington, Iowa, by whom the 

 type specimen was found. A physician by profession, he was a man of versatile talents, of 

 scientific habits, and an ardent lover of nature. His attention was attracted in the later 

 fifties to the extraordinary richness of the Burlington limestones in crinoidal remains, and he 

 was the first who began their systematic collection after the few obtained by Owen's expedi- 

 tion in 1848-49. It was through his influence that Wachsmuth became interested in the sub- 

 ject, and began in the field the studies which led to the numerous publications on the crinoids 

 with which his name was afterwards connected. 



Types. The original used in Hall's description is in the Museum of Comparative Zoology, 

 Harvard College. The other specimens figured are in the author's collection. 



Horizon and locality. Lower Carboniferous, Lower Burlington limestone ; Burlington, 

 Iowa — also reported by Keyes from Hannibal, Missouri. 



