216 PAL2E0NT0L0GY OF ILLINOIS. 



range three pieces, the two lateral of which are larger than the 

 other, and connect above, on their sloping sides, with brachial 

 pieces, while the middle piece between these is irregularly 

 hexagonal, and supports three very small pieces in the next 

 range, which connect with the anal opening and the vault 

 pieces above, and with the brachials on each side. 



Vault made up of a few comparatively large pieces, the 

 central one of which is a little more convex than the others. 

 Anal opening very small, lateral, or on about the same 

 horizon as the arm openings, and surrounded by only five 

 plates, which are not protuberant. Arm openings twelve, 

 small, arranged around the margin of the summit, three to 

 each of the two posterior rays, and two to each of the others. 

 Arms apparently, from the small size of the openings, and the 

 very small articulating surfaces for the first free arm pieces, 

 very slender and fragile. Column unknown. Height of body, 

 0.31 inch; breadth from the anal to the anterior side, 0.42 

 inch; breadth of base, 0.17 inch. 



In the concavity of the under side, and the incurved character of its first 

 anal and first radial pieces, this species presents much the appearance of a 

 Zeacrinus, though in the number and arrangement of the parts composing the 

 whole body, it will be seen to possess all the essential characters of the great 

 genus Actinocrinus, as it has been generally understood. We placed it provi- 

 sionally in the subgenus Amplwracrinus, in first describing it, on account of the 

 lateral position of the anal opening, but we subsequently became satisfied that 

 it differs sufficiently from the species of that group to be made the type of a 

 distinct geniis. It differs from Agaricocrinus in having comparatively much 

 larger first radial pieces, and very differently formed and arranged interradials, 

 as well as in the general form of its body, and its much weaker arms, which 

 are also located around the summit, instead of around the lower part of the 

 body. 



We are under obligations to Mr. Charles Wachsmuth. of Burlington, Iowa, 

 for the use of the only specimen of this species we have seen. 



Locality and position: Burlington, Iowa; Burlington limestone, of the 

 Lower Carboniferous series. 



