37 



bearing eighteen arms, we would say it is a distinct species. The 

 number of ambulacral openings to the vault is of the greatest 

 specific importance, but a crinoid, injured on any part of the body, 

 might have been able to heal the wound, by an abnormal growth, 

 restoration or intercalation of: plates. 



There are three plates, in each of three regular interradial 

 areas, one followed by two. In the area on the right of the 

 three-armed ray there are only two plates, one followed by another. 

 If we are correct in supposing the specimen illustrated to be ab- 

 normal, from some injury, then the areas, probably, are all alike 

 and have three plates, one followed by two. In the azygous area 

 there are seven plates. The first one is in line with the first 

 primary radials and larger than either one of them. It is fol- 

 lowed by four plates in the second range, and two in the third 

 range, one of which reaches the plates of the vault in the speci- 

 men illustrated. The first plate and the last plate may be abnor- 

 mal in size, and the latter, to some extent, in position; for if the 

 ray, on the right of the azygous area, in a normal condition bears 

 four arms, then the azygous area is, probably, cut off from the 

 vault, and the last plate shown in the illustration is much smaller 

 than it appears to be in the specimen, and does not extend to 

 the vault plates. 



The vault is conoidal and terminates in a large subcentral pro- 

 boscis. It is covered with numerous convex, polygonal plates. 



This species has little or no resemblance in form to B, casse- 

 dayannus or B. formaceus, the only seventeen- armed species 

 heretofore described, and seems to be as far removed from all 

 eighteen- armed species, except possibly, B. longirosiris ; but it is 

 so far removed from that species that no comparison will throw 

 any light upon either of them. 



Found in the Burlington Group, at Burlington, Iowa, and now 

 in the collection of S. A. Miller. 



BA.TOCRINUS SELECTUS, n. sp. 



Plate II, Fig. 3. azygous side; Fig. 4, opposite view; Fig. 5, 



summit. 



Species medium size. Calyx obconoidal, truncated only the size 

 of the column. Plates smooth, no radial ridges. Arm openings 

 directed upward and not visible in a basal view. 



