12 



gular, and supports three other smaller radials ; the two first are also 

 quadrangular, and the last pentangular, supporting two arms, which 

 bifurcate on the eighth plate, giving four arms to the anterior ray ; 

 on each of the anterio-lateral rays the second bifurcation takes place 

 on the sixth arm-plate from the second radial, one arm being simple 

 from this point to the end, but the other again bifurcating on the eighth 

 plate from the second bifurcation, making six arms from each of these 

 rays ; and as the posterior rays doubtless had the same number, the 

 whole number of arms was probably twenty-eight. The plates of the 

 calyx are marked by radiating ridges diverging from each plate to 

 the others, except within the basal depression, which is smooth. The 

 body-plates are also depressed at the angles, which gives it a still 

 more angular appearance. The second radials are constricted in the 

 middle, sharply angular on their backs, and truncated below, abruptly 

 sloping to the sutures between them and the first radials. The backs 

 of the arms, particularly on their lower parts, are very angular, with 

 deep depressions between them ; and small angular projections gar- 

 nish their sides where they abut together, giving them a serrated 

 and very angular appearance. Tentacles strong, not very closely 

 arranged. One specimen shows part of an inflated proboscis, which 

 is composed of small angular plates, and extended far up within the 

 arms. This species is too conspicuously different from any other to 

 need comparison. 



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

 stone, Burlington, Iowa. — Collections of Rev. W. H. Barris and B. J. 

 Hall, Esq. 



Zeacrinus sacculus (n. s.) Body subglobose, contracted at the 

 junction of the arms ; concavity of the base small, taking in but a 

 small part of the subradials ; basal plates small, covered by the last 

 joint of the column ; subradial plates six ; five of them reaching the 

 basal plates, one of which is large, being situated beneath the right 

 posterio-lateral ray ; the sixth smaller than the others, quadrangular, 

 not reaching the basal plates, and situated nearly beneath the 

 right anterio-lateral ray ; first radials broader than high, straight on 

 their upper sides, one hexagonal, three pentagonal, and one sub- 

 quadrangular, which last is on the right posterio-lateral ray ; second 

 radials much broader than high, their upper lateral angles depressed, 

 their upper central ones prominent ; four of them pentangular, sup- 

 porting two arms each; one quadrangular, supporting two other 

 small radials, the latter supporting two arms, which bifurcate once, 

 on the sixth or seventh plate from the fourth radial, giving four arms 

 to this ray ; each of the arms of the other rays bifurcate on the sixth 

 plate from the second radial, and a part of the arms rhus thrown off 

 bifurcate again farther up, giving six arms to each of these rays, — 

 twenty-eight arms in all. These abut together laterally, leaving but 



