-63 



gaping suture. A single, elongated, brachial or second radial, 

 rounded and contracted in the middle, and axilliary. supports 

 upon its superior sloping sides, m each radial series, the free 

 arms. The arms are long, slender, I'ound and corajjosed of 

 rather long plates which are slightly constricted in the middle 

 part. The first plates are longer than the succeeding ones. 

 The arms do not bifurcate and there are, therefore, only ten 

 arms in this species. Pinnules distant. 



Azygous plates are as usual in this genus; the first one is 

 pentagonal, about half as large as a subradial, rests upon the 

 upper sloping sides of two subradials and between the first ra- 

 dial, on the right, and the second azygous plate, on the left, 

 and is truncated, at the top, for the third azygous plate; the 

 second plate is pentagonal, about as large as the first, rests 

 upon the truncated upper end of a subradial, and between a 

 first radial, on the left, and the first and third azygous plates, 

 on the right, and is truncated at the ujiper end, for the fourth 

 plate. The fourth plate extends beyond the third. 



This species is distinguished by its small size, hemispherical 

 calyx, long, constricted brachials and ten arms. When com- 

 pared with P. rowleyi it will be noticed, tliat sjiecies has two 

 brachials, in some of the rays, and all the arms bifurcate toward 

 the top. It will not be mistaken, for any other species, by any 

 one capable of making a comparison. 



Found by the late Hon Wm. McAdams, who was a prominent 

 naturalist, in the St. Louis Group, at Alton, Illinois, and now 

 inthe collection of S. A. Miller. 



POTERIOCRINUS BROADHEADI. n. sp. 



Plate IV, Fig. 7, azygous side view,- Fig. 8, lateral vieiv. 



We have examined six specimens belonging to this S2iecies, 

 one a third larger than the specimen illustrated, three others 

 as much smaller, and each one is longer and larger upon the 

 azygous side than ujjon the opposite side, showing the unsym- 

 metrical form of the calyx is normal. Calyx irregularly obco- 

 noidal above the broad truncated base, by reason of the longi- 

 tudinal convexity of the plates and the dejjres.sed sutures, or 

 it might be called somewhat obiayramidal. The azygous side 

 is longer than the other, the two rays opposite the azygous 



