16 



the attachment of the column small, about half the diameter of the 

 cavity formed by the projecting rim ; first radial plates moderately 

 large, each having a prominent node occupying a large portion of 

 the surface of each, as also of the first anal plate ; second radials 

 short, about twice as wide as high ; third radials a little larger than 

 the second, and supporting one brachial plate on each of their upper 

 sloping sides, and they, in their turn, supporting two arms each, giving 

 the arm formula 14 = 20 arms. A more or less prominent ridge runs 

 along the centre of each ray from the nodes of the first radials, which 

 bifurcate on the third radials, and again on each brachial plate, 

 passing off to the base of each arm. Anal series, five ; inter-radial 

 series, three ; the lower one, which is the largest, is somewhat tumid, 

 forming a centre around which the radial ridges diverge. Dome 

 about as high as the depth of the body below the arms, covered by 

 numerous tumid plates, and surmounted by a central proboscis. 



This species somewhat resembles A. rusticus of Hall, with which 

 it is associated, but differs from that species in its more compact and 

 less pentalobate form, the number of arms to each ray, the arrange- 

 ment of the plates, and the surface-marking. 



Locality and position, in the upper division of the Burlington Lime- 

 stone, BurHngton, Iowa. — Collections of Mr. Charles Wachsmuth 

 and E,ev. W. H. B arris. 



AcTiNOCRiNUS Nashville Troost, var. suUractus. The upper 

 division of the Burlington Limestone, at Burlington, furnishes an 

 Actinocrinus which has the general appearance, and answers the 

 description, of A. Nashvillce (Troost), as given by Prof. Hall, in 

 the Iowa Reports, from the Keokuk Limestone, except that it gener- 

 ally lacks the supra-interradials, one only appearing in the only per- 

 fect specimen discovered, which is on the right postero-lateral ray, 

 this position indicating an irregularity. Another specimen shows a 

 single supra-interradial ; but the specimen is too imperfect to deter- 

 mine to which ray it belongs. This slight or non-development of 

 supra-interradials is not regarded of specific importance, although 

 the form and appearance are thereby considerably modified. — My 

 own collection and that of Mr. Charles Wachsmuth. 



Genus Megistocrinus Owen and Shumard. 

 Megistocrinus plenus (n. s.) Body subglobose, a little broader 

 than high, base rather narrow, somewhat regularly rounded ; basal plate 

 prominent, extending considerably below the first radials ; cicatrix, 

 for the attachment of the column rather large, slightly concave, from 

 the margin of which the plate is bevelled abruptly to the sutures 

 between it and the first radials ; first radials hexagonal, a little wider 

 than high ; second radials smaller than the first, about as wide as 



