ACTINOCRINID^. 617 



and 1 plate. Ventral disk conical, almost as high as the dorsal cup ; grad- 

 ually passing into the anal tube. The plates of the disk grow smaller as 

 they approach the arm bases ; the orals and radial dome plates larger and 

 strongly nodose ; the intervening smaller ones slightly tumid. Anal tube 

 stout and long, extending considerably above the tips of the arms, and com- 

 posed of small, tumid plates. The joints of the stem vary considerably in 

 width ; some of the nodal joints in the upper part are near!}' three times as 

 wide as the interiiodals, and are provided with knife-like edges, while the 

 edges of the internodals are but very little convex. 



Horizon and Locality. — Lower Burlhigton limestone ; Burlington, Iowa. 



Types in the collection of Wachsmuth and Springer. 



Cactocrinus multibrachiatus Hall. 

 Plate LVI. Fig. 6 and 7, and Plate LVIII. Fig. 8. 



1858. AcUmcrimis multibrachiatus— nkiA.; Geol. Eep. Iowa, Vol. I., Part II., p. 5S0, Plate 10, Fig. 10. 

 1881. Actinocrimis multibrachiatus — W. and Sp. ; Revision Palfeocr., Part II., p. 144. 



Syn. Actinocrimis multibrachiatus Tar. ecUnutus Hail; Descr. NeirSpec. Crin., p. 10. 



Calyx gradually and evenly spreading to the bases of the free arms, dis- 

 tinctly truncated at the lower end, and slightly depressed between the rays 

 at the arm regions. The ventral disk fully one third lower than the dorsal 

 cup, and surmounted by a moderately large, almost central tube. Plates of 

 the dorsal cup all marked by strong radiating ridges jDroceeding to the sides 

 of the plates, and meeting in the centre, where they form a conspicuous 

 angular node, which is transverse upon the radials and costals. The ridges 

 passing up and down the radials and brachials are more prominent than any 

 of those proceeding to, or coming from, the interbrachials. Between the 

 radials and basals there are three such ridges, or four where the former rest 

 upon two basals, while the other plates have but one to each side. 



Basals short, their lower margins projecting outward, forming a sharp rim, 

 which extends beyond the sides of the column, and is deeply notched at the 

 sutures. Radials nearly as long as wide. First costals one third smaller than 

 the radials, three of them hexangular, the two posterior ones generally 

 pentangular; second costals a little smaller than the first. Distichals still 

 smaller, and all axillary ; the outer ones supporting an arm, which is free 

 from the second or third plate ; the inner ones two palmars, of which again 

 the inner one in both divisions of the ray is axillary, and supports two arms; 

 the outer one is truncated, and followed by one arm ; all arm-bearing plates 



78 



