FOSSILS OF THE BUELINGTOX GROUP. 399 



die one. The intermediate spaces are occupied by much 

 smaller and less prominent pieces. Opening nearly over 

 the posterior side, and penetrating a very prominent thick- 

 ened ridge, which extends from the middle to the anal 

 side, and is composed of comparatively large pieces for this 

 part. 



Surface of all the plates, including those of the vault, 

 regularly granular. Column of moderate size, round, and 

 composed near the base of alternately thicker and thinner 

 pieces, with radiately striated surfaces, and perforated by a 

 very small nearly rounded central canal. 



Hight of body to top of vault, 0.88 inch; breadth, includ- 

 ing three brachial pieces on each side, 1.13 inches ; breadth 

 of concavity of under side, 0.57 inch; thickness of column, 

 0.40 inch; from base, 0.17 inch. 



This species differs from all the others yet known from the Burling- 

 ton group, in having three arms to each posterior ray. It is most nearly 

 allied to A. bullatus, Hall, a single individual of which, out of a consid- 

 erable number in Mr. WACHSMUTH'S collection, has abnormally three 

 arms in one of the posterior rays, all the others having two to each ray 

 all around. It differs also from all of these, however, as well as from 

 the original type now before us, in having the concavity of the under 

 side less deep, and all the pieces surrounding it more tumid, while the 

 form and proportions of its body pieces are different, its anal region 

 much more protuberant, and its vault pieces less rounded and swelled. 

 Its surface is also more coarsely granular. 



Locality and position Highest part of the upper bed of the Burling- 

 ton group, at Burlington, Iowa. Lower Carboniferous. Xo. 146 of Mr. 

 collection. 



GENUS TAXOCRIXUS, Phillips, 1843. 

 TAXOCEIXUS THIEMEI, Hall (sp.) 



PI. 4, Fig. 1. 

 Forbesiocrinus Thiemei, HALL. Desc. Xew Crin.. Prelim. Note, p. 8, 18C1. 



( A perfect specimen of this beautiful species, showing the arms complete and about five inches 

 of the column. Burlington limestone, Burlington, Iowa. Mr. WACIISMUTU'S collection.) 



